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In this paper we report on the synthesis of a composition, Ti3Al(C0.5,N0.5)2, belonging to the Mn+1AXn family of ternary layered carbides and nitrides. X-ray and selected area diffraction confirm that this compound is isostructural with Ti3SiC2; its a and c-lattice parameters are 3.0404(5) and 18.414(6) Å, respectively. Chemical analysis performed by electron dispersive and electron energy loss spectroscopy confirmed the Ti3AlCN chemistry. Using a synchrotron radiation source and a diamond anvil cell, we also measured the pressure dependencies of the lattice parameters. Up to a pressure of ≈50 GPa, no phase transformations were observed. The bulk modulus is 219±4 GPa, with a pressure derivative, Ko′, of 3.7±0.3. We also fabricated the ternary Ti3AlC2, with some Sn [nominal composition Ti3(AlSn0.2)C2]. Its a and c-lattice parameters are 3.0804(7) and 18.5426(7) Å, respectively. Its bulk modulus is 226±3 GPa, with a pressure derivative, Ko′, of ≈4. In both cases, the compressibility was greater along the c than along the a axes. We also show that in the case of Tin+1AlCn MAX-phases, replacing C by N results in a decrease in both lattice parameters and bulk moduli. The apparent contradiction inherent in this observation can be reconciled by assuming that the addition of N results in the formation of vacancies on the Al and/or X-sites. [ABSTRACT FROM AUTHOR]

A series of perovskites Sr 3– x Ca x Fe 2 TeO 9 (0 ≤ x ≤ 1) have been prepared in polycrystalline form by solid–state reaction method in air. These materials have been studied by X–ray powder diffraction method (XRPD) and Raman spectroscopy. An analysis of the XRD patterns at room temperature has shown that these compounds crystallize in a tetragonal system, space group I 4/ m. The structure contains alternating (Fe/Te) 2a O 6 and (Fe/Te) 2b O 6 octahedra, tilted in anti–phase in the basal ab–plane. The study of Raman spectroscopy at various temperatures shows a transition from tetragonal to cubic phase: I 4/ m → Fm 3 ¯ m . This phase transition occurs at high–temperature. Analysis of Raman spectra recorded at several temperatures shows that this phase transition appears near ∼375 °C for ( x = 0), ∼435 °C for ( x = 0.5) and ∼451 °C for ( x = 1). A proportional and gradual increase of temperature phase transition is observed as function of the calcium amount. [ABSTRACT FROM AUTHOR]

Structures of Sr 2−x Ca 1+x TeO 6 double perovskites have been studied by the profile analysis of X-ray diffraction data and Raman spectroscopy at room temperature. This series adopts a monoclinic symmetry for the compositions (0 ≤ x ≤ 0.5) with P 2 1 / n as space group and a triclinic system with P 1 ¯ space group for the compositions (0.5 < x ≤ 2). These results were confirmed by the observed tolerance factor calculated from the distances obtained from the Rietveld refinements which indicates that the true tilt system for the compositions range (0.5 < x ≤ 2) is the triclinic tilt system. Clear changes in the Raman modes centered at 600, 610 and 620 cm −1 and the FWHM of O Te O bending vibrations, centered at 738 cm −1 confirmed that the triclinic symmetry takes place between the compositions x = 0.5 and x = 1. Furthermore, Raman spectroscopy studies at high temperature were done for Ca 3 TeO 6 . For this compound, considerable changes in the temperature dependence of the modes were well illustrated. [ABSTRACT FROM AUTHOR]

Chemically modified carbon paste electrode (CPE) for cadmium (II) analysis has been constructed by mixing KPb 4−x Ca x (PO 4 ) 3 (0 ≤ x ≤ 1.5) (CaLA) and graphite powder. The lacunar apatite was synthesized using solid reaction and characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and Raman spectroscopy. The refinement study was carried out using Rietveld method where the obtained results show a good agreement between the observed and calculated patterns. The detection of cadmium (II) was investigated in acetate buffer (pH 4.5) using differential pulse anodic stripping voltammetry (DPASV). The limit of detection obtained under the optimized experimental conditions was 5.35 × 10 −7 mol L −1 with a relative standard deviation of 2.37%. Possible interferences were tested and evaluated in 5.0 × 10 −5 mol L −1 cadmium (II) in the presence of other inorganic ions. Finally, the proposed method was successfully applied to determine cadmium (II) in seawater and mussel samples. Hence, the satisfactory results confirm the applicability of this sensor in practical analysis. [ABSTRACT FROM AUTHOR]

Sr 2 Zn 1−x Ni x WO 6 solid solutions (with 0 ≤ x ≤ 1) have been synthesized by solid-state reactions, and characterized by X-Ray diffraction and Raman spectroscopy. The X-Ray powder diffraction (XRD) data at room temperature shows a systematical change of structure vs. nickel content: the compound adopts a monoclinic phase with a P 2 1 /n space group with 0 ≤ x ≤ 0.18, a tetragonal structure with a I 4/ m space group with x = 0.25, and a tetragonal structure with a I 4/ mmm space group with 0.5 ≤ x ≤ 1. Further in-situ Raman study at elevated temperature (up to 555 °C) shows the pristine monoclinic phase (0 ≤ x ≤ 0.18) follows the phase path: monoclinic ( P 2 1 /n ) → tetragonal ( I 4/ m ) → tetragonal ( I 4/ mmm ) → cubic ( Fm 3 ¯ m ); for the compound Sr 2 Zn 0.75 Ni 0.25 WO 6 , it involves later two phase transitions as tetragonal ( I 4/ m ) → tetragonal ( I 4/ mmm ) → cubic ( Fm 3 ¯ m ); and for the 0.5 ≤ x ≤ 1 compounds, only one phase transition I 4/ mmm to Fm 3 ¯ m was observed. The combined investigation of composition and temperature provides us a complete understanding of chemical substitution and temperature effect on structural phase transition. [ABSTRACT FROM AUTHOR]

[Ba 2 CaWO 6 ] 1− x [Sr 2 CaWO 6 ] x (0≤ x ≤1) materials were synthesized by the high temperature solid state reaction and firing methods, and characterized using techniques of X-ray diffraction and Raman spectroscopy. The crystal structures were determined by Rietveld refinements on the laboratory X-ray powder diffraction data. As a function of composition, upon increasing the strontium content, the samples exhibit a sequence of three phase transitions: from cubic ( Fm 3 ̅ m ) to tetragonal ( I 4/ m ) to monoclinic structural phases ( I2/m , P2 1 /n ). These transitions have been confirmed by Raman studies Fm 3 ¯ m x = 0 → I 4 / m 0.1 ≤ x ≤ 0.2 → I 2 / m 0.3 ≤ x ≤ 0.5 → P 2 1 / n 0.6 ≤ x ≤ 1 Furthermore, increasing the temperature for the compositions [Ba 2 CaWO 6 ] 1− x [Sr 2 CaWO 6 ] x (0.1≤ x <1), manifests the P 2 1 / n to I 2/ m , the I 2/ m to I 4/ m and the I 4/ m to Fm 3 ̅ m phase transitions. For the compositions (0.1≤ x ≤0.2) the tetragonal to cubic phase transition is well illustrated. For the room temperature I 2/ m monoclinic compositions, two phase transitions were observed for all the compositions with x ranging from 0.3 to 0.5: from the monoclinic ( I 2/ m ) to tetragonal ( I 4/ m ), and from I 4/ m to Fm 3 ̅ m structures. Finally, for the room temperature P 2 1 /n monoclinic compositions, only two phase transitions are observed in the temperature range probed by Raman spectroscopy, the temperature was not high enough to reach the tetragonal-to-cubic phase transition. [ABSTRACT FROM AUTHOR]

A new chemically modified electrode was synthesized for the determination of mercury(II) using differential pulse anodic stripping voltammetry (DPASV). The electrode was modified by lacunar apatite K 1− x Na x CaPb 3 (PO 4 ) 3 (0 ≤ x ≤ 1) synthesized using solid reaction. These powders were crystallized in the hexagonal system, space group P6 3 /m. The effect of sodium content on structural, thermodynamic and electrochemical properties of prepared apatite has been studied. Therefore, the best results was obtained using NaCaPb 3 (PO 4 ) 3 ( x = 1) as modifier of carbon paste electrode for the electrochemical detection of mercury(II). The later ions were preconcentrated on the surface of the modified electrode and oxidized at 0.06 V vs. Ag/AgCl. The electroanalytical procedure comprises of two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse voltammetry. The different parameters that govern the two steps were optimized. A linear response was obtained in the concentration range from 1.0 mol L −1 × 10 −4 mol L −1 to 2.0 mol L −1 × 10 −7 mol L −1 Hg(II) after activation of the electrode surface under the optimized conditions. The standard deviation was evaluated in a high and low concentration of mercury(II). The values ​​obtained for seven consecutive measurements were 1.24% and 5.07% of 1.0 mol L −1 × 10 −4 mol L −1 and 5.0 mol L −1 × 10 −6 mol L −1 mercury(II) solutions respectively. The detection limit and quantification limit for mercury(II), calculated from nine times standard deviation of blank/slope of the calibration graph, were 1.086 mol L −1 × 10 −8 mol L −1 and 3.62 mol L −1 × 10 −8 mol L −1 , respectively. The proposed chemically modified electrode was applied to determine mercury(II) in seawater samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis and characterization of new double perovskites Ba2−x Sr x MgTeO6 (0⩽ x ⩽2). [•] High temperature studies of Ba2−x Sr x MgTeO6 double perovskite using Raman spectroscopy. [•] Temperature and compositions induced phase transitions in these materials. [•] Structural determination/refinement of these compounds as a function of composition. [Copyright &y& Elsevier]

Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O-Te-O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis and characterization of Ba2−xSr x MWO6 (M=Ni, Co and 0⩽ x ⩽2) double perovskites. [•] High temperature studies of these double perovskite using Raman spectroscopy. [•] Temperature and compositions induced phase transitions in these materials. [•] Structural determination/refinement of these compounds as a function of composition. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report high-temperature (up to 550°C) Raman spectroscopy of phase transitions in Sr2MWO6 (M=Zn, Co) double perovskite oxides. For Sr2ZnWO6 modes centered at 137cm−1, 152cm−1, merge around 80°C. The same behavior was observed for the 436cm−1 and 447cm−1 modes. The mode centered at 854cm−1 shows a change in the slope at the same temperature, thus indicating a first order phase transition from the monoclinic (P21/n) to tetragonal (I4/m) structure. With increasing temperature, a little change in the slope of the temperature dependence of mode centered at 855cm−1 is observed around 480°C which might be a sign of the second phase transition in Sr2ZnWO6 (tetragonal (I4/m) to cubic (Fm-3m)). The temperature dependence of the full width at half maximum (FWHM) of the most intense modes in Sr2ZnWO6 spectra was studied. The width behaves linearly as a function of temperature with a break observed in the slope of the width of the modes at 80°C; thus, showing the first phase transition occurrence. For Sr2CoWO6 the transition from tetragonal (I4/m) structure to cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of modes centered at 438cm−1 and 845cm−1. The transition was observed around 420°C. [Copyright &y& Elsevier]

Abstract: X-ray diffraction and Raman spectroscopy studies of Sr doped double perovskites compound Ba2−x Sr x ZnWO6 with (0≤ x ≤2) were investigated. As a function of composition while increasing strontium amount, the samples show two phase transitions from cubic to tetragonal phase and from tetragonal to monoclinic structure. Both Rietveld refinements and Raman studies showed that the first phase transition occurs between x =1 and 1.2; the second phase transition is observed around x =2. Furthermore, increasing the temperature for the compositions (1.2≤ x <2), manifests the tetragonal to cubic phase transition. For x =2 two phase transitions were observed as a function of temperature. For this series, the phase transitions are illustrated by considerable changes in the composition and temperature dependence of the modes. All the Raman modes show a linear behavior when the composition or temperature is increased, then the slope change indicating the symmetry change. [Copyright &y& Elsevier]

Abstract: In this work we report on the crystal structure and Raman spectroscopy of BaSrMWO6 (Mg) double perovskite oxides. The results showed that the Ni, Co and Mg containing compounds crystallize in a cubic system with the space group Fm-3m. The double perovskite structure can be represented as a three-dimensional network of alternating MO6 and WO6 octahedra, with Ba- and Sr-atoms occupying the interstitial spaces. The Raman spectra of this crystalline perovskite oxides are interpreted by means of factor group analysis in terms of space group Fm-3m. Assignments of the Wonal stretching and bending modes have been made. High temperature Raman spectroscopy of BaSrNiWO6 showed that all lattice modes illustrate a linear decrease in wavenumbers while temperature is increased. No discontinuities, in the temperature changes, in wavenumber observed for all modes recorded: indicating that the structure remains cubic and stable up the highest temperature studied here. [Copyright &y& Elsevier]

Abstract: The new solid solution series Ba3−x Sr x (VO4)2 (0≤ x ≤3) has been synthesized and studied by a combination of X-ray powder diffraction and Raman vibrational spectroscopy. This continuous solid solution crystallise in the hexagonal system with space group. The structure has been determined at room temperature from X-ray diffraction by the Rietveld method analysis. It is formed by a 3D network of (Ba/Sr)(1)(VO4)2 4− layers linked into a crystal network by (Ba/Sr)2+ (2) cations. The vibrational spectra of this crystalline orthovanadate solid solution series are interpreted by means of factor group analysis in terms of space group (). Assignments of the V–O vibrational stretching and bending modes, as well as some of the external modes, have been made. While all the modes show a monotonous shift as a function of the composition x, a break in the curves of intensities, full width at half maximum and band areas as a function of x is observed and attributed to the statistical distribution of Ba and Sr ions in the same crystallographic sites. [Copyright &y& Elsevier]

Abstract: In this paper, we report on high temperature Raman spectroscopy studies (up to 550°C) of the phase transitions in Sr2BWO6 (B=Ni, Mg) double perovskite oxides. For both compounds, the transition from the tetragonal (I4/m) phase to the cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of the modes. To better view this phase transition, the FWHM temperature dependence of the most intense modes were studied; by this study, we have obtained a sensitive guide to the onset of the phase transition. A large increase of the FWHM with increasing temperature is observed for all modes in the spectrum, clear transitional effects were observed: the width behaves in a linear way as a function of temperature; when the temperature reached around 300°C, a drop in the width of this mode was observed; thus, showing the phase transition occurrence for both compounds. This drop is much more illustrated in Ni-containing compound than in Sr2MgWO6. [Copyright &y& Elsevier]

Abstract: Using a synchrotron X-ray radiation source and a diamond anvil cell we measured the dependences of the lattice parameters on quasi-hydrostatic pressure of the order of 50 GPa of the following MAX phases: Ti2InC, (Ti0.5,Zr0.5)2InC, Zr2InC and Ti2SnC, Nb2InC and Hf2InC. Like other MAX phases, the phases studied herein were all stable up to ≈50 GPa. In both series, the substitution of by the larger sized metals, Zr or Nb (with varying between 1.34 and 1.55 Å) resulted in larger unit cell parameters and volumes. At 152±3 and 148±3 GPa, the respective bulk moduli, , of Ti2SnC and Ti2InC are quite comparable. Replacing Ti by Hf or Nb in Ti2SnC leads to increases in by 11% and 18%, respectively. Conversely, replacing half the Ti by Zr in Ti2InC leads to a 13% drop in ; replacing all of the Ti drops it by 16.5%. Most of these trends are reproduced in our ab initio calculations of . For all compositions, the compressibilities along the -direction were greater than those along the -direction. For the M2SnC series, the compressibilities along the -axes were quite similar; the compressibilities along the -axis of Ti2SnC were greater than in the Nb- or Hf-containing ternaries. The -axis compressibilities of the In-containing compounds were almost indistinguishable. The compressibilities along the -axes of (Ti0.5,Zr0.5)2InC and Zr2InC were also quite comparable; those of Ti2InC was less compressible. [Copyright &y& Elsevier]

Abstract: High-pressure investigations of NaCo(H2PO3)3·H2O dihydrogenphosphite, in diamond anvil cell have been performed at room temperature using in situ Raman spectroscopy. The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. Group theory yields to 69Ag +69B1g +69B2g +69B3g Raman active modes for NaCo(H2PO3)3·H2O, of which only 36 bands are observed at ambient conditions. The pressure-induced phase transition sequence of NaCo(H2PO3)3·H2O dihydrogenphosphite to pressures up to 20GPa was explored. Raman spectra showed that the investigated compound, NaCo(H2PO3)3·H2O, compressed smoothly up to 4.2GPa and starts amorphizing at 6.8GPa. The amorphous phase persists down to 1atm upon release of pressure. The amorphization was due to a chemical decomposition and also might be due to pressure-induced distortions of the lattice upon compression associated with the Na+ and Co2+ cation displacements and strongly coupled with rigid rotations of the (PO3) units. No P–H vibrations were seen after pressure release which means that P–H bonds were broken. The frequencies seen in the Raman spectra for the amorphous phase are characteristic of (PO4)3− or tetrahedral short-range structure. [Copyright &y& Elsevier]

Abstract: Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3GeC2 sample up to a pressure of 51GPa. No phase transformations were observed. Like Ti3SiC2, and most other compounds belonging to the same family of ternary carbides and nitrides, the so-called MAX phases, the compressibility of Ti3GeC2 along the c axis is greater than that along the a axis. The bulk modulus is 197±4GPa, with a pressure derivative of 3.4±0.1. We also characterized Ti3GeC2 by infrared spectroscopy; four of the five expected infrared modes were observed for this material. [Copyright &y& Elsevier]

Abstract: The lattice parameters of Ti2AlN and Ti2AlC powders were measured as a function of pressure up to ≈50GPa, using a synchrotron radiation source and a diamond anvil cell. No phase transformations were observed. As for most related layered carbides and nitrides, such as Ti4AlN3 and Ti3SiC2, the compressibilities of Ti2AlN and Ti2AlC along the c-axes are larger than those along the a-axes. The bulk modulus of Ti2AlC at 186±2GPa, is ≈10% higher than that of Ti2AlN at 169±3GPa. [Copyright &y& Elsevier]

Abstract: High-pressure investigations of SrNi3(P2O7)2 pyrophosphate, in diamond anvil cell have been performed at room temperature using in situ Raman spectroscopy and X-ray synchrotron radiation source. The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. Group theory yields to 60 Raman active modes 30Ag+30Bg for SrNi3(P2O7)2, of which only 37 bands are observed at ambient conditions. The pressure-induced phase transition sequence of SrNi3(P2O7)2 pyrophosphate to pressures up to 61.5GPa was explored. Raman spectra showed that the investigated compound, SrNi3(P2O7)2, compressed smoothly up to the highest investigated pressures, transforms to another structure at pressures of 50.5GPa. The new high-pressure phase persists metastably down to 1atm. upon release of pressure. We also measured the pressure dependence of the lattice parameters of the polycrystalline SrNi3(P2O7)2 sample up to a pressure of 48GPa. The compressibility of SrNi3(P2O7)2 along the b-axis is larger than that along the a-axis. At 48GPa, a and b cell parameters are almost equal indicating that a phase transition from the monoclinic to a tetragonal structure started. The bulk modulus of SrNi3(P2O7)2 (P21/c) is 124±2GPa with a pressure derivative of 4.37±0.12. [Copyright &y& Elsevier]

Sr 3 Fe 2+ x Mo 1− x O 9−3 x /2 (0.3 ≤ x ≤ 1.0) ceramics were synthesized in the polycrystalline form using a solid-state reaction. Characterizations of all the synthesized compounds were done using elemental analysis, XRD, Mössbauer and UV–Vis spectroscopic techniques. This series adopts two phase transitions: I 4/ mcm → Pm –3 m → P 4/ mmm. The Mössbauer spectra indicate the presence of paramagnetic behavior and some magnetic ordering. The direct band gap energy increases from 1.70 to 2.25 eV with increasing Fe content. [Display omitted] Perovskite-type oxides Sr 3 Fe 2+ x Mo 1− x O 9−3 x /2 (x = 0.30, 0.45, 0.60 0.75, and 1.00) were synthesized in the polycrystalline form using a solid-state reaction route in the air. These materials have been studied at room temperature using the techniques of XRD, Mössbauer and UV–visible spectroscopies. The crystal structures were resolved by the Rietveld refinement method and revealed that this series adopts two phase transitions from a tetragonal I 4/ mcm phase (x = 0.30, 0.45 and 0.60) to a simple cubic Pm –3 m phase (x = 0.75), to another tetragonal P 4/ mmm phase (x = 1.00). The values of the isomer shift (IS) and quadrupole splitting (QS) confirm that the formal oxidation state of the iron contained in our compounds consist of mixed valence Fe3+ and Fe4+ cations for the octahedral environment. The Mössbauer spectrum of the SrFe 0.917 Mo 0.083 O 3−δ (x = 0.75) sample is consistent with the iron atom in a cubic lattice site. The direct band gap energy increases from 1.70 to 2.25 eV with increasing Fe content. Plots of optical parameters, such as absorption coefficient, refractive index, extinction coefficient, optical conductivity, real and imaginary parts of the dielectric function, electric modulus and complex impedance, were achieved in the photon energy range 1.54–4.94 eV by means of UV–vis spectrophotometry experiments. [ABSTRACT FROM AUTHOR]

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a recently discovered phase, Ta4AlC3. This phase adopts a hexagonal structure with the space group P63/mmc; at room conditions, the a and c parameters are 3.087(5) and 23.70(4) Å, respectively. Up to a pressure of 47 GPa, no phase transformations were observed. Like Ta2AlC, but unlike many related phases such as Ti4AlN3, Ti3SiC2, Ti3GeC2, and Zr2InC, the compressibility of Ta4AlC3 along the c and a axes are almost identical. The bulk modulus of Ta4AlC3, 261±2 GPa, is ≈4% greater than that of Ta2AlC. Both, however, are ≈37% lower than the 345±9 GPa of TaC. [ABSTRACT FROM AUTHOR]

We measured the volume thermal expansion of Ti3SiC2 from 25° to 1400°C using high-temperature X-ray diffraction using a resistive heated cell. A piece of molybdenum foil with a 250 μm hole contained the sample material (Ti3SiC2+Pt). Thermal expansion of the polycrystalline sample was measured under a constant argon flow to prevent oxidation of Ti3SiC2 and the molybdenum heater. From the lattice parameters of platinum (internal standard), we calculated the temperature by using thermal expansion data published in the literature. The molar volume change of Ti3SiC2 as a function of temperature in °C is given by: VM (cm3/mol) = 43.20 (2)+9.0(5) x 10-4T+1.8(4) x 10-7T2. The temperature variation of the volumetric thermal expansion coefficient is given by: αv(°C-1)=2.095 (1) x 10-5+7.700 (1) x 10-9 T. Furthermore, the results indicate that the thermal expansion anisotropy of Ti3SiC2 is quite mild in accordance with previous work. [ABSTRACT FROM AUTHOR]

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti4AlN3 sample up to a pressure of 55 GPa. No phase transformations were observed. As observed in Ti3SiC2, Ti3Si0.5Ge0.5C2, and Zr2InC, the compressibility of Ti4AlN3 along the c axis was larger than along the a axis which leads to a decrease in the c/a ratio with increasing pressure. The bulk modulus is 216±2 GPa, with a pressure derivative of 3.84±0.06. [ABSTRACT FROM AUTHOR]

Using a synchrotron-radiation source and a diamond-anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Zr2InC sample. Up to a pressure of 52 GPa, no phase transformations were observed. As observed in Ti3SiC2 and Ti3Si0.5Ge0.5C2, the compressibility of Zr2InC along the c axis was greater than along the a axis. The bulk modulus is 127±5 GPa, with a pressure derivative of 4.25±0.3; the former is in excellent agreement with our ab initio calculations (130.9 GPa). The a (3.367 Å) and c (15.100 Å) parameters from the ab initio calculations are also slightly larger than those measured here, viz., 3.35 and 14.91 Å. Surprisingly, a hysteresis was observed in the a-lattice parameters; they were higher upon unloading than loading. The reason for this hysteresis is not clear at this time. [ABSTRACT FROM AUTHOR]

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3Si0.5Ge0.5C2 sample. Up to a pressure of 53 GPa, no phase transformations were observed. As for the isostructural hexagonal Ti3SiC2, the compressibility along the c axis was greater than along a. The bulk modulus is 183±4 GPa with a pressure derivative of 3.4±0.2. This work shows that the replacement of Si by Ge in Ti3SiC2 results in a systematic decrease in the bulk moduli. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An innovative approach was adopted to improve the energy storage and dielectric properties of Bi 0.5 Na 0.5 TiO 3 (BNT) ceramics by incorporating a glass additive. The chosen Na 2 O–Bi 2 O 3 –TiO 2 –P 2 O 5 (NBTP) glass shares a similar atomic composition to minimize any alteration of the crystalline structure and the build-up of impurities. Simultaneously, we investigate the feasibility of offsetting Bi and Na losses during the synthesis process. XRD and Rietveld refinement analysis confirmed the formation of pure BNT phases with no secondary phases. Dielectric parameters were evaluated in the frequency range of 1 Hz to 1 MHz, over a wide temperature range of 30 °C–270 °C, showing minimal variation in their values for the composites with lower glass content. Our findings indicate a notable reduction in grain size and the sintering temperature with improved relative density, leading to enhanced energy storage and efficiency in BNT-based ceramics. The composite with 2.5 wt% glass content shows the highest recovered energy of 154.9 mJ/cm3 with an energy efficiency of 88.64 %, making it particularly promising for advanced capacitor technology. [ABSTRACT FROM AUTHOR]

The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications. [ABSTRACT FROM AUTHOR]

Polycrystalline Sr2ZnWO6 is prepared by staged calcination of stoichiometric amounts of SrCO3, ZnO, and WO3 in air (Al2O3 crucible, 1. [ABSTRACT FROM AUTHOR]

Due to the low capacity, low working potential, and lithium coating at fast charging rates of graphite material as an anode for Li-ion batteries (LIBs), it is necessary to develop novel anode materials for LIBs with higher capacity, excellent electrochemical stability, and good safety. Among different transition-metal oxides, AB2O4 spinel oxides are promising anode materials for LIBs due to their high theoretical capacities, environmental friendliness, high abundance, and low cost. In this work, a novel, porous Zn0.5Mg0.5FeMnO4 spinel oxide was successfully prepared via the sol–gel method and then studied as an anode material for Li-ion batteries (LIBs). Its crystal structure, morphology, and electrochemical properties were, respectively, analyzed through X-ray diffraction, high-resolution scanning electron microscopy, and cyclic voltammetry/galvanostatic discharge/charge measurements. From the X-ray diffraction, Zn0.5Mg0.5FeMnO4 spinel oxide was found to crystallize in the cubic structure with Fd 3 ¯ m symmetry. However, the Zn0.5Mg0.5FeMnO4 spinel oxide exhibited a porous morphology formed by interconnected 3D nanoparticles. The porous Zn0.5Mg0.5FeMnO4 anode showed good cycling stability in its capacity during the initial 40 cycles with a retention capacity of 484.1 mAh g−1 after 40 cycles at a current density of 150 mA g−1, followed by a gradual decrease in the range of 40–80 cycles, which led to reaching a specific capacity close to 300.0 mAh g−1 after 80 cycles. The electrochemical reactions of the lithiation/delithiation processes and the lithium-ion storage mechanism are discussed and extracted from the cyclic voltammetry curves. [ABSTRACT FROM AUTHOR]

The title compounds are characterized by powder XRD and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Raman spectra of synthetic HfSiO4 were determined to pressures of 38.2 GPa. Changes in the spectra indicate that HfSiO4 undergoes a room-temperature phase transition from the hafnon structure (I41/amd space group) to the scheelite structure (I41/a space group) at a pressure of ∼19.6 GPa. Upon release of pressure to ambient conditions, the spectra indicate that the sample retains the scheelite structure. Zircon has been classified previously as the least compressible tetrahedrally coordinated silicate known. However, pressure derivatives of the peak positions in hafnon are smaller than those in zircon, and suggest that hafnon is more incompressible than zircon. Furthermore, the pressure derivatives also suggest that the high-pressure, scheelite-structured HfSiO4 phase is more incompressible than the scheelite-structured ZrSiO4 (reidite). Thus, the post-hafnon phase appears to be even more incompressible than hafnon, which would make it the least compressible tetrahedrally coordinated silicate known to date. [ABSTRACT FROM AUTHOR]

This study focused on the production and characterization of phosphate glass fibers (PGF) for application as composite reinforcement. Phosphate glasses belonging to the system 52P2O524CaO13MgO (11-(X + Y)) K2OXFe2O3YTiO2 (X:1, 3, 5) and (Y:0.5, 1) were elaborated and converted to phosphate glass fibers. First, their mechanical properties and chemical durability were investigated. Then, the optimized PGF compositions were used afterward as reinforcement for thermosetting composite materials. Polyester matrices reinforced with short phosphate glass fibers (sPGF) up to 20 wt % were manufactured by the contact molding process. The mechanical and morphological properties of different sPGF-reinforced polyester systems were evaluated. The choice between the different phosphate-based glass syntheses (PGFs) was determined by their superior mechanical performance, their interesting chemical durability, and their high level of dispersion in the polyester matrix without any ad sizing as proven by SEM morphological analysis. Moreover, the characterization of mechanical properties revealed that the tensile and flexural moduli of the developed polyester-based composites were improved by increasing the sPGF content in the polymer matrix in perfect agreement with Takayanagi model predictions. The present work thus highlights some promising results to obtain high-quality phosphate glass fiber-reinforced polyester parts which can be transposed to other thermosetting or thermoplastic-based composites for high-value applications. [ABSTRACT FROM AUTHOR]

In this paper, we focus on understanding the behavior of the temperature dependence of electrical resistivity (ρ) and magnetoresistance (MR) in Sr 3 Fe 2+ x Mo 1– x O 9–3 x /2 perovskites with x = 0.45, 0.60, and 1.00. Three polycrystalline materials were synthesized using conventional solid-state reaction techniques. Rietveld analysis of room-temperature X-ray diffraction data reveals that all three compositions crystallize in tetragonal symmetry; where x = 0.45 and 0.60 undergo an I 4/ mcm space group, while x = 1.00 adopts a P 4/ mmm space group. Electrical resistivity measurements carried out at magnetic fields (0 and 1 T) reveal the presence of a transition from the ferromagnetic phase to the paramagnetic phase in the vicinity of the T MI. The metal-insulator transition temperature (T MI) decreases with increasing Fe content and rises slightly with changing magnetic field from 0 to 1 T. The magnetoresistance (MR) of the SrFeO 3–δ sample (x = 1.00) has a large value of about 63.6 %, indicating that it can be exploited for certain devices. A variety of theoretical models are used to study the behavior of electrical resistivity in various temperature ranges, showing excellent agreement with experimental results. • High-quality samples were prepared by solid-state reaction. • All samples exhibit a ferromagnetic to paramagnetic phase transition. • The M-I transition temperature decreases with increasing Fe content. • MR reached 63.6% for sample SrFeO 3-δ (x = 1). • Three theoretical models were used to study resistivity behavior. [ABSTRACT FROM AUTHOR]

In this work, the structural, electronic, magnetic, and electrical properties of tri-layered SrMO3/BaTiO3/SrMO3 (M = Ru and Os) have been investigated using first-principles calculations based on density functional theory in the framework of GGA + U. The interfacial separation work indicates that the studied tri-layers are energetically stable. Moreover, the simultaneous presence of spontaneous polarization and magnetization with matallic characteristics was predicted. In addition, the electrical and thermal conductivities as a function of temperature are obtained using the semi-classical Boltzmann transport theory. The obtained results make the studied systems promising materials for spintronic applications. [ABSTRACT FROM AUTHOR]

Due to their structural stability and flexibility, perovskite oxides have paved their way as oxygen evolution reaction (OER) electrocatalysts. The in-depth understanding of the limiting factors toward good activity and fast charge transfer are still considered as major challenges for highly active OER perovskite catalysts. In this work, we disclose the changes in the perovskite structure and properties that influence the activity as we introduce new criteria to be considered for perovskites electrocatalysts design. The activity test of the series Sr 1-x La x Ti 1-x Fe x O 3 (0.2 ≤ x ≤ 0.8) reveals the overpotential of 300 mV @ 10 mA.cm−1, and Tafel slop of 57.6 mV dec−1, as the lowest values corresponding to the composition x = 0.4. As function of the composition, the dielectric constant is found to decrease from 3000 (x = 0.2) to 953 (x = 0.4), and increases up to 5497 (x = 0.8). This variation of the dielectric constant is found to influence the activity of the catalysts where lowest overpotential of 300 mV @ 10 mA.cm−1 is found for x = 0.4 with the smallest dielectric constant. The phase transition detected in the perovskite series upon substitution has induced a distortion in the unit cell, which is found to be in alignment with the evolution of the overpotential in the perovskites series. The distortion has induced a preferable octahedra orientation for efficient OER reaction, this orientation correspond to the interatomic distance (1) = 1.89 Å and (2) = 2.04 Å (x=0.4) with the condition of (1) remains shorter than (2). The band gap, thus the conduction and valence bands edges, is found to decrease with the increase of the interatomic distance (Fe/Ti-O) and with the deviation of the Bond angle (B)-O2-(B) from the ideal value of 180°. These findings put light on the limiting factors of the perovskites activity by linking the structural parameters and the physical properties with the objective of accurately designing highly-efficient perovskite OER electrocatalysts. [Display omitted] • The dielectric constant depends on the interatomic distance through BO 6 re-orientation; • Shorter (1) than (2) creates preferred orientation boosting the OER; • High catalytic activity is observed at low dielectric constant; • The conductivity increases with increasing Fe3+ and La3+ incorporation; • The band gap decreases with increasing the interatomic distance (Fe/Ti-O) value; [ABSTRACT FROM AUTHOR]

Lead-free relaxor ferroelectric Na 0·5 (Bi 1-x Nd x) 0.5 TiO 3 (xNdNBT, x = 0–30%) ceramics were synthesized using the conventional solid-state method. Detailed Rietveld refinement revealed transitions from rhombohedral (x = 0, 5%), to a coexistence of R 3 c and Pnma symmetries (x = 10, 15%), followed by a tetragonal P 4/ mmm phase for the high Nd-concentrations (x = 25, 30%). High-temperature dielectric stability was found over a large temperature range (for instance ±15% from -90 °C to 405 °C for x = 30%) with very low dielectric losses, especially at high temperatures. The substitution of Bi3+ by Nd3+ results in a perturbation of the ferroelectric order and favors short-range polar regions in the system. From the ferroelectric measurements, we demonstrated the stabilization of a coexistence of non-ergodic and ergodic relaxor state or ergodic relaxor state at specific doping concentrations. Besides, high-energy storage properties were obtained at high temperatures, with W rec > 1.15 J/cm3 in the temperature range 140 °C–200 °C for the 5NdNBT and a moderate W rec between 0.5 and 0.77 J/cm3 in a large temperature range from 25 °C to 200 °C and with high efficiency >70% for 10NdNBT composition. In addition, a high electrocaloric response (ΔT = 1.8 K at 95 kV/cm) was found using the indirect method for the 5NdNBT composition, with great temperature stability below 20% over a broad temperature range (80–140 °C) and with a high ΔT/ΔE > 0.19 K m/V. The obtained electrocaloric response was related to the thermal evolution of the polar regions in mixed ergodic and non-ergodic relaxor states under an applied electric field. [ABSTRACT FROM AUTHOR]

Polycrystalline manganite powders of Ba 1-x Bi x Ti 1-x Mn x O 3 (x = 0, x = 0.1 and x = 0.2) were synthesized by the conventional solid-state reaction process. Their crystal structure, morphological, optical, dielectric and electrical properties were investigated. X-ray diffraction of the prepared samples was made at room temperature and confirmed the formation of a perovskite phase. Structural refinement, using the Rietveld method, revealed a tetragonal P 4 mm phase of pure BTO and a tetragonal P 4/ mmm phase with the presence of vacancies for both doped samples (x = 0.1 and x = 0.2). Scanning electron microscopy indicated that the perovskite samples had a grain size smaller than 1 μm. From UV–vis–NIR spectra, we found that the band gap reduces from 3.29 eV to 1.48 eV with the increase of Bi and Mn amounts, resulting in a shift of the absorption wavelength region toward the visible range. Dielectric analysis was conducted in a wide range of temperatures at different frequencies. Phase transitions were identified from thermal dielectric results, showing that the samples exhibited a non-relaxor behavior. The structural transformation from tetragonal to cubic structure corresponding to the transition from ferroelectric phase to paraelectric phase was observed in the dielectric properties investigation. The complex impedance spectroscopy indicated the presence of grain and grain boundary effects in the conduction mechanism. Electrical analysis showed that doping with Bi and Mn enhanced the DC conductivity. Furthermore, the DC conductivity temperature dependence confirmed that the studied samples present a semiconductor behavior. The activation energies of grain and grain boundaries depended on the amount of incorporated Bi and Mn. The activation energy of grain varied between 0.54 and 0.87 eV suggesting that the DC electrical conductivity is governed by ionized oxygen vacancies. The activation energy of grain boundaries varied between 0.85 and 0.58 eV. [ABSTRACT FROM AUTHOR]

In this work structural refinement, complex impedance spectroscopy (CIS) and Raman spectroscopy have been investigated on Na 0.5 (Bi 1-x Dy x) 0.5 TiO 3 (xDyNBT) ceramic systems with x = 0, 2, 5 and 15%. The pure NBT, 2DyNBT and 5DyNBT compounds crystallize in a rhombohedral R3c structure while the 15DyNBT composition crystallizes in an orthorhombic Pnma structure. We reported that dysprosium addition affects the phase transition temperatures as well as the dielectric losses. The electrical transport at high temperatures was investigated using the CIS over a wide frequency range (10–106 Hz). The studied samples showed a non-Debye type process, with a short-range relaxation for the pure NBT and a coexistence of both localized and long-range relaxations of charge carriers for the 2DyNBT and 5DyNBT compounds. For the high concentration, 15DyNBT, a short-range relaxation is observed. Moreover, using a brick-layer model we discuss the resistance and capacitance of the different contributors (grain and grain boundaries) in our samples. High temperature Raman spectroscopy investigation was performed in order to follow the temperature evolution of the structural transformations on ferroelectric compounds. Anomalies in the temperature evolution of the vibrational modes are seen to correlate well with the temperature transitions observed from dielectric measurements. [ABSTRACT FROM AUTHOR]

Abstract In this work, Na 0.5 (Bi 1- x Dy x) 0.5 TiO 3 (0 ≤ x ≤ 15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy3+ into Sodium Bismuth Titanate (Na 0.5 Bi 0.5 TiO 3) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (∆ ɛ / ɛ (150 °C) ≤ ± 15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2 J/cm3 obtained for 2%Dy composition at 200 °C. The obtained results are very promising for energy storage capacitors operating at high temperatures. [ABSTRACT FROM AUTHOR]

Layered oxides are regarded as promising cathode materials for sodium-ion batteries. We present Na 2/3 Co 1/2 Ti 1/2 O 2 as a potential new cathode material for sodium-ion batteries. The crystal features and morphology of the pristine powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The cathode material is evaluated in galvanostatic charge-discharge and galvanostatic intermittent titration tests, as well as ex-situ X-ray diffraction analysis. Synthesized by a high-temperature solid state reaction, Na 2/3 Co 1/2 Ti 1/2 O 2 crystallizes in P2-type structure with P 6 3 / mmc space group. The material presents reversible electrochemical behavior and delivers a specific discharge capacity of 100 mAh g −1 when tested in Na half cells between 2.0 and 4.2 V (vs. Na + /Na), with capacity retention of 98% after 50 cycles. Furthermore, the electrochemical cycling of this titanium-containing material evidenced a reduction of the potential jumps recorded in the Na x CoO 2 parent phase, revealing a positive impact of Ti substitution for Co. The ex-situ XRD measurements confirmed the reversibility and stability of the material. No structural changes were observed in the XRD patterns, and the P2-type structure was stable during the charge/discharge process between 2.0 and 4.2 V vs. Na + /Na. These outcomes will contribute to the progress of developing low cost electrode materials for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Transition metal-based AB 2 O 4 -type spinel oxides were extensively reported as promising anodes for lithium-ion batteries (LIBs). In this study, the manganese doped Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 (x = 0, 0.25, 0.5, 0.75, 1, and 1.25) porous spinel oxides were synthesized as anode materials for LIBs by a facile sol-gel synthesis method. X-ray diffraction analysis revealed the formation of a pure cubic spinel structure with the Fd 3 ̅ m space group for all compounds, while the cubic Fd 3 ̅ m symmetry of all samples was confirmed by Raman scattering spectroscopy. From scanning electron microscopy, it was evident that the synthesized spinels are interconnected nanoparticles that exhibit a face-centered cubic, highly crystalline, thermally very stable, and nanosized microporous morphology. Electrochemical properties of lithium-ion batteries (LIBs) anodes made of Mn-doped spinel ferrites were investigated by charge/discharge cycling of the LIBs. It is found that Mn doping led to a significant enhancement of the performance stability during the discharge-charge process, with excellent cycling stability and good rate capability for the compound where x = 1, maintaining a specific capacity at 307 mAh g−1 after 50 cycles. The Li-ion storage mechanism was examined by cyclic voltammetry measurements at various scan rates. The present study suggests eco-friendly, inexpensive, and efficient spinel oxides as suitable alternative anode materials for LIBs. • Manganese-doped porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels prepared by sol-gel method. • Porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 samples show the Fd 3 ̅ m cubic spinel structure. • Synthesized Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels exhibit a macroporous morphology. • Porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels as anodes for LIBs were investigated. • Mg 0.9 Zn 0.1 FeMnO 4 shows a reversible capacity of 307 mAh g−1 after 50 cycles. [ABSTRACT FROM AUTHOR]

Transition metal-based AB 2 O 4 -type spinel oxides were extensively reported as promising anodes for lithium-ion batteries (LIBs). In this study, the manganese doped Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 (x = 0, 0.25, 0.5, 0.75, 1, and 1.25) porous spinel oxides were synthesized as anode materials for LIBs by a facile sol-gel synthesis method. X-ray diffraction analysis revealed the formation of a pure cubic spinel structure with the Fd 3 ̅ m space group for all compounds, while the cubic Fd 3 ̅ m symmetry of all samples was confirmed by Raman scattering spectroscopy. From scanning electron microscopy, it was evident that the synthesized spinels are interconnected nanoparticles that exhibit a face-centered cubic, highly crystalline, thermally very stable, and nanosized microporous morphology. Electrochemical properties of lithium-ion batteries (LIBs) anodes made of Mn-doped spinel ferrites were investigated by charge/discharge cycling of the LIBs. It is found that Mn doping led to a significant enhancement of the performance stability during the discharge-charge process, with excellent cycling stability and good rate capability for the compound where x = 1, maintaining a specific capacity at 307 mAh g−1 after 50 cycles. The Li-ion storage mechanism was examined by cyclic voltammetry measurements at various scan rates. The present study suggests eco-friendly, inexpensive, and efficient spinel oxides as suitable alternative anode materials for LIBs. • Manganese-doped porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels prepared by sol-gel method. • Porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 samples show the Fd 3 ̅ m cubic spinel structure. • Synthesized Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels exhibit a macroporous morphology. • Porous Mg 0.9 Zn 0.1 Fe 2−x Mn x O 4 spinels as anodes for LIBs were investigated. • Mg 0.9 Zn 0.1 FeMnO 4 shows a reversible capacity of 307 mAh g−1 after 50 cycles. [ABSTRACT FROM AUTHOR]

In this work, experimental investigation of structural, morphological, magnetic, dielectric, electrical, and optical properties of cobalt-doped PbTi 1−x Co x O 3-δ perovskite materials (0 ≤ x ≤ 0.4), synthesized by the solid-state reaction method, was reported. X-ray diffraction measurements revealed the tetragonal perovskite structure with the P 4 mm space group for all the samples. The SEM images showed a decrease in the average grain size from 1.23 to 0.11 µm as cobalt dopant amount increases. The magnetic hysteresis loops sufficiently indicated the antiferromagnetic character for all the synthesized samples. At room temperature, the dielectric constant exhibited a decrease with the increasing Co amount. However, both the dielectric constant and dielectric loss increased with temperature without the appearance of any phase transition from room temperature to 380 °C. The σ ac plots versus frequency showed an increase, according to the Jonscher power law. Complex impedance results demonstrated the semiconducting nature for all the ceramics through the presence of the negative temperature coefficient of resistivity. For all samples, the transport properties of charge carriers were found to be thermally activated. Thermal evolution of the σ dc for all the compounds was described by the Arrhenius law. The transport mechanism was found governed by the electrons resulting from the ionization of the oxygen vacancies. The optical results of all compounds showed strong absorption in the whole visible range. The optical band gap energy was found in the semiconducting range 2.98–1.12 eV. • Cobalt-doped lead titanate PbTi 1−x Co x O 3-δ prepared by solid-state reaction. • X-ray diffraction measurements indicate the P4mm tetragonal perovskite structure. • The magnetic hysteresis loops reveal the antiferromagnetic character for all samples. • The cobalt substitution affects the dielectric and electrical properties of the samples. • Impedance spectroscopy demonstrates the semiconducting nature for all samples. • The optical band gap energy was found in the semiconducting range 1.46–1.12 eV. [ABSTRACT FROM AUTHOR]

Abstract: Crystal structures from two new phosphates Na4NiFe(PO4)3 (I) and Na2Ni2Fe(PO4)3 (II) have been determined by single crystal X-ray diffraction analysis. Compound (I) crystallizes in a rhombohedral system (S. G: R-3c, Z =6, a =8.7350(9)Å, c =21.643(4)Å, R 1 =0.041, ). Compound (II) crystallizes in a monoclinic system (S. G: C2/c, Z =4, a =11.729(7)Å, b =12.433(5)Å, c =6.431(2)Å, β =113.66(4)°, R 1 =0.043, ). The three-dimensional structure of (I) is closely related to the Nasicon structural type, consisting of corner sharing [(Ni/Fe)O6] octahedra and [PO4] tetrahedra forming [NiFe(PO4)3]4+ units which align in chains along the c-axis. The Na+ cations fill up trigonal antiprismatic sites within these chains. The crystal structure of (II) belongs to the alluaudite type. Its open framework results from [Ni2O10] units of edge-sharing [NiO6] octahedra, which alternate with [FeO6] octahedra that form infinite chains. Coordination of these chains yields two distinct tunnels in which site Na+. The magnetization data of compound (I) reveal antiferromagnetic (AFM) interactions by the onset of deviations from a Curie–Weiss behaviour at low temperature as confirmed by Mössbauer measurements performed at 4.2K. The corresponding temperature dependence of the reciprocal susceptibility χ −1 follows a typical Curie–Weiss behaviour for T >105K. A canted AFM state is proposed for compound (II) below 46K with a field-induced magnetic transition at H ≈19kOe, revealed in the hysteresis loop measured at 5K. This transition is most probably associated with a spin-flop transition. [ABSTRACT FROM AUTHOR]

The ceramics with perovskite structure of the compositions Ba 1-x Bi x Ti 1-x Fe x O 3 (x = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized through the conventional solid-state reaction route. All prepared samples were characterized by X-ray diffraction, Raman spectroscopy, UV–visible spectroscopy and impedance spectroscopy. The X-ray diffraction characterization at room temperature indicated the formation of perovskite phase in all the samples. The X-ray diffraction data refined by Rietveld technique revealed two phase transitions with the increase of BiFeO 3 content, the first structural transformation from tetragonal (P 4 m m) to cubic (P m 3 ‾ m) and the second from cubic (P m 3 ‾ m) to rhombohedral (R 3 c), which were confirmed by Raman spectroscopy. UV–vis absorption spectra of doped compounds indicated the presence of four electronic transitions in octahedrally coordinated Fe3+ ions from their fundamental 6A 1g (S) level to different excited levels. The co-doping of Bi3+ and Fe3+ ions from 0% to 80 mol% leads to a decrease of the direct band gap energy from 3.29 to 1.91 eV, and a shift of the band gap edges, namely the conduction band minimum and valence band maximum. The impedance results suggest that both grain (G) and grain boundary (GB) contribute to the total conductivity and the effect of this latter increases with (Bi, Fe) content. Additionally, the Nyquist plots showed the negative temperature coefficient of resistance (NTCR) and the temperature-dependent dc electrical conductivity demonstrated the semiconducting nature for all samples. The sample x = 0.4 exhibited the highest dc electrical conductivity. The activation energy values revealed that the conduction mechanism is dominated by ionized oxygen vacancies. The changes of dielectric properties at room temperature with increasing BiFeO 3 -doping amount are discussed. • Design of Ba 1-x Bi x Ti 1-x Fe x O 3 (0 ≤ x ≤ 0.8) by solid-state reaction process. • Their structural, optical and electrical properties are investigated in detail. • Prepared materials can be used for visible-light photocatalysis applications. • Electrical properties indicate the semiconducting nature for all samples. • The conduction mechanism of the ceramics is dominated by ionized oxygen vacancies. [ABSTRACT FROM AUTHOR]

• Synthesis and characterization of the new perovskites composition with the chemical formula Ba 0.198 La 0.784 Ti 0.096 Fe 0.8 O 3-δ. • The composition effect on the morphology and the atomic structure. • The Optical responses and the type of band gap of the new perovskites materials. • Ba 0.198 La 0.784 Ti 0.096 Fe 0.8 O 3 - δ magnetic response at 300 K and 10 K. • ZFC and FC mode of Ba 0.198 La 0.784 Ti 0.096 Fe 0.8 O 3 - δ perovskite material. We report the observation of superparamgnetic behavior induced by the substitution La3+ by Ba2+ at A-sites and Fe+3 by Ti4+ at B-sites. Ba 0.198 La 0.784 Ti 0.096 Fe 0.8 O 3 - δ was synthesized via solid state reaction. The Rietveld refinements revealed an orthorhombic (Pbnm). The low-mag STEM results showed that the particles were found to exhibit square like shape and formed in single crystal with high degree of crystallinity. The particle size ranges of 50−300 nm. Element mapping demonstrates a complementary distribution between Ba and La, while homogenous distribution is found for Fe and O. The optical band gap determined from UV–vis analysis is equal to 1.93 eV which is smaller than the reported one for LaFeO 3 and BaTiO 3. The hysteresis loops at 300 K and 10 K show superparamagnetic behavior, which deviate extremely from the antiferromagnetic nature of LaFeO 3 perovskite. The temperature dependent magnetization demonstrates that the material kept a net magnetization of 12.29 (emu/g) at very low temperature. [ABSTRACT FROM AUTHOR]

In this work, X-ray diffraction assisted with Rietveld refinement method was used to study the effect of the composition on the structural transitions and the optical properties of perovskite ABO 3 -type, prepared using the conventional solid state reaction technique. X-ray analysis indicates the ability of BaTiO 3 to accommodate different percentages of La3+ cation in A-sites and Fe3+ cation in B-sites while maintaining the ABO 3 -type structure. Rietveld refinement method showed the existence of several phase transitions: a first from tetragonal (0 ≤ x ≤ 0.25) to cubic (0.3 ≤ x ≤ 0.6) and a second from cubic (0.3 ≤ x ≤ 0.6) to orthorhombic (0.7 ≤ x ≤ 1), with one tetragonal sub-transition (P 4 mm → P 4/ mmm) and one orthorhombic sub-transition (Pnma → Pbnm). The UV–vis analysis showed that BaTiO 3 absorption band undergoes an expansion up to 592 nm as the amount of La3+ and Fe3+ increases. The structural investigation revealed that B O B bond angle has an effect on the band gap values as small values were found for bonds angles close to 180°. As the amount of the substitution increases, a shift of both the conduction band minimum and valence band maximum was observed for all the compositions, which is consistent with the band gap values obtained. • Synthesis and characterization of Ba 1-x La x Ti 1-x Fe x O 3 (0≤x≤1) solid solution. • Demonstration of two main structural phase transition in BLTF (0≤x≤1) system. • Observation of the optical absorption expansion from the UV domain up to 592 nm of the visible domain. • The reveal of B-O-B bond angle parameter effect on the decrement of the optical band gap. • Visualization of a downward shift of the CBM and upward shift of the VBM. [ABSTRACT FROM AUTHOR]

The crystal structure, morphological, optical, electrical and dielectric properties of polycrystalline perovskites of Ba 1-x Bi x Ti 1-x Mn x O 3 (x = 0.3 and x = 0.4), prepared by the standard solid-state reaction process, were investigated systematically. From the X-ray diffraction results at ambient temperature, both samples showed the pure perovskite phase. Rietveld refinements revealed that the studied compounds adopt the cubic structure symmetry with P m 3 ‾ m as a space group. Scanning electron microscopy demonstrated that the samples show irregularly spherical grains with an average size of 2 μm. From UV–vis–NIR absorption spectra, the synthesized compounds exhibit a maximum absorbance in the whole visible range. Furthermore, the direct band gap energy was found to be 1.07 and 0.85 eV for x = 0.3 and 0.4, respectively. The electrical transport in these materials was studied by using the impedance spectroscopy from the room temperature to 110 °C. The modelling of complex impedance data was performed to separate the grain and grain-boundary contributions in the conduction process. The addition of Bi and Mn ions increased the dc electrical conductivity. The thermal variation of the dc electrical conductivity proved the semiconductor behavior of both studied compounds. The obtained activation energies from the dc conductivity for grain and grain-boundary contributions were found to be 0.39–0.36 eV for x = 0.3 and 0.20–0.32 eV for x = 0.4. The conduction mechanism was explained by hopping process along ionized oxygen vacancies. The dielectric permittivity and dielectric loss of both compositions showed an increase with increasing temperature. • Design of novel manganite perovskites Ba 1-x Bi x Ti 1-x Mn x O 3 with x = 0.3 and 0.4 by solid-state reaction route. • Structural, optical, electrical and dielectric properties of the polycrystalline perovskites are investigated. • Optical properties of the materials reveal they can be used for visible-light photocatalysis applications. • Both compounds show the presence of grain and grain boundary effects in the conduction mechanism. • Electrical conductivity of the ceramics indicates they can be used for fuel cells applications. [ABSTRACT FROM AUTHOR]