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We show that the spin reorientation transitions in Nd2CuO4 are associated with the polaronic states and depend on the electronic interactions between the bulk and the surface.

Here we report the evidence of an additional magnetic ordering and frequency dispersive magneto-dielectric (MD) permittivity besides multiferroic behavior in Te4+ (S = 0) doped FeVO4. Two antiferromagnetic transitions similar to FeVO4 at ∼21.86 K (T N 1 ) and 16.03 K (T N 2 ) were observed in all samples. An additional novel defect clusters based magnetic ordering at relatively higher temperature (T A M O ) ∼ 203 K is also observed from the magnetization. Evaluated magnetic moments show systematic decrease and the magnetic frustration factors show an increase with the increasing of Te4+ (S = 0) content. MD studies show stable ferroelectric ordering at spiral magnetic transition (T N 2 ) and the multiferroic order persists to the largest doping of Te (x = 0.10). The MD studies also reveal a magneto-capacitive (MC) behavior at T A M O (∼203 K) with a high dielectric constant and loss, and the possible reason for the magnetic ordering and MC behavior is ascribed to short range magnetic clustering arising out of defect based mechanisms. Mössbauer spectroscopic studies confirm local structural correlation with magnetic and ferroelectric ordering.

La0.7Sr0.3MnO3 (LSMO)/poly(vinylidenefluoride-co-trifluoroethylene)(P(VDF-TrFE) particulate nanocomposite films prepared to produce large magnetoelectric (ME) voltage at room temperature for multifunctional device applications. LSMO nanoparticles (NPs) were prepared by sol–gel auto-combustion method and these NPs belong to space group R-3c. LSMO/P(VDF-TrFE) (0–3) nanocomposite (NC) films were prepared by solution casting method for different volume percentage of LSMO in P(VDF-TrFE). Dielectric and DC leakage current density(J) analysis of these NCs reveal very small loss tangents (~ 0.01) and very small leakage current density J ~ 10−7 A/mm2 respectively, which further demonstrate the uniform distribution of NPs in P(VDF-TrFE) matrix. Room temperature M-H and low temperature M-T analysis of LSMO NPs confirm ferromagnetic nature with Curie temperature at ~ 368 K. LSMO/P(VDF-TrFE) NC films exhibit multiferroic properties up to 5% volume percentage of LSMO at room temperature. A maximum ME voltage 11.68 mV is produced corresponding to giant transverse ME voltage coefficient ( $${\alpha }_{31}^{V})$$ = 155.74 mVOe−1 cm−1 at DC magnetic field (Hdc) = 2.57 kOe and AC magnetic fileld(Hac) = 25Oe for 0.5% LSMO volume percentage NC films. A self bias ME voltage 11.3175 mV is observed at zero Hdc for 0.5% LSMO volume percentage NC films, which can be used inpotential ME devices.The variation of ME voltage coefficient $$\left({\alpha }^{V}\right)$$ at different angles between P and applied magnetic field(Hdc) for 0.5% LSMO NC films is also reported which shows $${\alpha }^{V}$$ is maximum at the angles 90o and 270o.

Here, we report detailed studies on magnetic phase transitions and magneto-electric (ME) coupling in $$\text {Fe}_{1-x}\text {Ce}_x\text {VO}_4$$ . X-ray diffraction (XRD) and Raman spectroscopic measurements confirm triclinic crystal structure (P-1) with small variation in lattice parameters and Ce incorporation into the $$\text {FeVO}_4$$ lattice up to 10% of Ce. The presence of local lattice distortions and electronic inductive effect in $$\text {FeVO}_4$$ between $$\text {Fe}^{3+}$$ and $$\text {V}^{5+}$$ ions were found in X-ray absorption near edge structure (XANES) studies due to the presence of $$\text {Fe}^{3+}$$ –O– $$\text {V}^{5+}$$ linkages. Two antiferromagnetic (AFM) transitions similar to $$\text {FeVO}_4$$ appear at 21.86 K and 16.03 K, and Ce doping has little effect on the magnetic transitions. $$^{57}\text {Fe}$$ Mossbauer spectroscopic results show the invariance of Fe valance. Low temperature high magnetic field Mossbauer data depicts the presence of spiral AFM order in all the samples. A sharp peak at 16.0 K in dielectric permittivity with minimal suppression due to applied magnetic field is observed indicating the presence of ferroelectricity and magneto-dielectric coupling. Magnetic and ME transitions are almost robust against Ce doping.

The effect of La-doping on the crystallographic structure and the Raman line-shape of CeO2 has been investigated. X-ray diffraction analysis suggests that the lattice parameter and the Ce/La–O bond...

The polycrystalline powder samples of PrCrO3 have been prepared using conventional solid-state synthesis method. Structural investigations are carried out using Raman spectroscopy and synchrotron X-ray diffraction (SXRD) followed by Rietveld refinement of diffraction data. Investigations of diffraction data suggest that these samples possess centrosymmetric orthorhombic structure with space group $$Pnma$$ $$(or\;Pbnm)$$ . The valence (charge) state of Cr in PrCrO3 has been determined from X-ray absorption near edge spectroscopy (XANES). Optical properties are studied using diffuse reflectance spectroscopy technique. Optical absorption study reveals that absorption in PrCrO3 ceramic is dominated by d–d electrons of chromium cation (Cr3+). The synthesized compound found to have energy bandgap of 3.20 eV. Based on the results observed, energy level diagram for PrCrO3 has been presented. High dielectric permittivity $$(\varepsilon {^{\prime}})$$ of the order $$3\times {10}^{3}$$ is observed for the studied sample. Impedance spectroscopy measurement at room temperature on sintered pellet indicates electronic inhomogeneity in the samples as demonstrated by the presence of dielectric relaxation processes associated with highly conducting grain and low conducting grain boundaries. The relaxation mechanism has been explained on the basis of Cole–Cole model. Observed high dielectric permittivity $$(\varepsilon {^{\prime}})$$ and optical energy bandgap $$({E}_{g})$$ indicates that PrCrO3 may find promising application in optoelectronic devices.

The effect of improved dielectric properties in the presence of an applied magnetic field is discussed in Pr doped polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$ complemented by the structural properties down to 50 K and magnetic properties. Enhanced dielectric permittivity and low dielectric loss represent the strongly field-dependent dielectric behaviour of the sample. The structural characterizations using synchrotron angle dispersive X-ray diffraction confirm the orthorhombic symmetry of the polycrystalline sample with the Pnma space group from 300 K to 50 K. There is no structural transition at lower temperatures up to 50 K; however the Mn O octahedral distortion is reduced. The investigation of dielectric properties for frequencies range 500 Hz to 1 MHz was conducted in the temperature range 8 K to 300 K with and without a magnetic field of 7 Tesla, which shows the high dielectric constant in the 500 Hz frequency region. This confirms the relaxation phenomena in polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$. ac conductivity data shows the increasing trend for frequencies along with the activation energy which increases from low frequencies to higher frequencies. Temperature-dependent dc magnetization study shows the negative magnetization in polycrystalline Gd$_{0.55}$Pr$_{0.45}$MnO$_3$ at low temperature at 100 Oe applied field, due to spin canting of Mn-Mn magnetic lattice. High coercivity due to competition in between spin ordering of Mn and Gd,Pr magnetic lattice at 5 K are also observed in the field-dependent magnetization study., Comment: 33 pages, 9 figures, 3 tables

A spark-plasma sintered ${\mathrm{GdCrO}}_{3}$ (SPS-GCO) is found to stabilize in its ferroelectric phase beyond room temperature. The intrinsic nature of this room-temperature ferroelectricity is established using ferroelectric positive-up--negative-down measurements and supported through piezoresponce force microscopy measurements. The SPS-GCO undergoes antiferromagnetic ordering at much lower temperatures, only below $\ensuremath{\approx}170\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Thus, any role of magnetism to the observed room temperature ferroelectricity in SPS-GCO can be ruled out. This is contrast to the concomitant antiferromagnetic and ferroelectric ordering observed below $\ensuremath{\approx}170\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in ${\mathrm{GdCrO}}_{3}$ (GCO) (prepared using standard solid-state synthesis technique). Using detailed Rietveld refinements of room-temperature x-ray diffraction patterns, SPS-GCO is found to stabilize in the noncentrosymmetric orthorhombic $Pna{2}_{1}$ space group (the reported low-temperature ferroelectric phase in GCO), while GCO stabilizes in the centrosymmetric $Pbnm$ space group at room temperature. Using first-principles calculations, we investigated the relative energies among various possible structures of ${\mathrm{GdCrO}}_{3}$ and found that the orthorhombic $Pna{2}_{1}$ and $Pbnm$ space groups are the most stable structures. The ferroelectric $Pna{2}_{1}$ phase of SPS-GCO (stabilized at room temperature using the high-pressure and high-temperature spark-plasma sintering process) undergoes transition to the paraelectric centrosymmetric phase upon heating beyond $\ensuremath{\approx}450\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ (as confirmed using dielectric and calorimetric measurements), which on subsequent cooling to room temperature does not undergo a transition back to the ferroelectric phase and remains in the centrosymmetric $Pbnm$ phase.

$\beta$-Ag$_2$Se is a promising material for room temperature thermoelectric applications and magneto-resistive sensors. However, no attention was paid earlier to the hysteresis in the temperature dependence of resistivity ($\rho$($T$)). Here, we show that a broad hysteresis above 35 K is observed not only in $\rho$($T$), but also in other electronic properties such as Hall coefficient ($R_H$($T$)), Seebeck coefficient, thermal conductivity and ultraviolet photoelectron spectra (UPS). We also show that the hysteresis is not associated with a structural transition. The $\rho$($T$) and $R_H$($T$) show that $\beta$-Ag$_2$Se is semiconducting above 300 K, but metallicity is retained below 300 K. While electronic states are absent in the energy range from the Fermi level ($E_F$) to 0.4 eV below the $E_F$ at 300 K, a distinct Fermi edge is observed in the UPS at 15 K suggesting that the $\beta$-Ag$_2$Se undergoes an electronic topological transition from a high temperature semiconducting state to a low temperature metallic state. Our study reveals that a constant and moderately high thermoelectric figure of merit ($ZT$) in the range 300-395 K is observed due to the broad semiconductor to metal transition in $\beta$-Ag$_2$Se., Comment: 6 pages, 4 figures, 1 table

In this report, the isothermal time-dependent Raman scattering study has been used to investigate the origin of the cluster glass state in samarium orthoferrites (SmFeO3) via probing selective dyna...

A comparative microstructural study of as sintered and rubbed surfaces of BaTiO3 (BTO) ceramic pellet has been carried out using lab (8 keV Cu-Kα) as well as synchrotron (8–19 keV) based powder x-ray diffraction (XRD) at room temperature. These studies show a drastic change in the surface-microstructure of the BTO ceramics. Just a minutes rubbing of the BTO ceramics on a rough surface causes broadening of diffraction peaks. Nearly 3-times increase in the peak width and ∼ 3-times increase in integrated peak intensity of (00l) type peaks has been observed. The changes were analyzed as rubbing induced (00l) texturing and occurrence of anisotropic strain with maxima along [00l]. High temperature XRD studies reveal that for the strained BTO grains, the tetragonal to cubic transformation does not initiates at the proper TC ∼120 °C and does not complete even at temperatures ∼ 350 °C, which is ∼ 3 times the normal TC. About 20% of the tetragonal phase still remains untransformed. These features have been attributed to the formation of strain-glass phase at the rubbed surface of the BTO ceramics.

The present work reports the study of four layer Aurivillius compound Bi 5 FeTi 3 O 15 (BFTO) with V 5+ (≤50%) doping at B-site ( F e 3 + , T i 3 + ). This is considered to be equivalent of increasing the magnetic ion ( F e 3 + ) concentration from 25% to 37.5%. Phase purity of the samples is confirmed with lab and synchrotron based x-ray diffraction measurements. The temperature dependent magnetization measurements indicate the paramagnetic nature of BFTO down to 2 K and the development of long-range antiferromagnetic (AFM) ordering with V 5+ doping. It is observed that the AFM Neel transition temperature ( T N ) decreases with increase of V 5+ doping. The presence of iron oxide impurity phases is excluded from the 57 Fe Mossbauer spectroscopy measurements. Temperature dependent dielectric constant measurements show the relaxation behaviour in highly doped samples.

Here we introduce a way to understand the phenomena of localization/delocalization of excitons experimentally as well as by first-principle study. Using in-situ temperature-dependent optical absorption spectroscopy (TD OAS), variation of delocalization parameter (ξ) and electronic disorder in terms of Urbach energy as a function of temperature was estimated. For this purpose, polycrystalline samples of PrFe1−xCrxO3 (x = 0 to 0.25) were synthesized via wet chemical method. The ξ increased with inclusion of Cr doping, which could be understood in terms of an increase in delocalized nature of excitons. Further, the theoretically simulated optical absorption spectrum for undoped and Cr-doped PrFeO3 clearly indicated the change in excitonic peak from almost Gaussian to Lorentzian nature and was explained in terms of an increase in delocalized nature of excitons with inclusion of Cr doping. Thus, using the combination of TD OAS and first-principle calculations, we demonstrated a way to acquire precise information about exciton dynamics, which could be very helpful in understanding many interesting phenomena such as electron–phonon coupling, electronic disorder near band edge and transport properties.

A detailed magnetic study on the Fe substituted NdCrTiO5 is presented. Phase purity of polycrystalline NdCr0.5Fe0.5TiO5 prepared by conventional solid-state technique has been confirmed by synchrotron X-ray diffraction (SXRD). Temperature-dependent magnetization (MT) measurements indicate a transition to an antiferromagnetic (AFM) type of magnetic ordering at T N ∼ 10 K. AFM type of order is also supported by magnetocaloric data. Magnetic hysteresis as well as a type of magnetic relaxation behavior collected below T N (at 5 K) indicate the presence of weak ferromagnetism.

The composition dependent dielectric and optical absorption measurements have been carried out on polycrystalline samples of PrFe1-xCrxO3 (x = 0 to 0.20) in order to investigate the possible correlation between (i) dielectric loss; defined in terms of loss tangent (tanδ) (ii) optical band gap (Eg) and (iii) width of electronic disorder i.e. Urbach width (Eu). It has been observed that with increasing Cr doping, the value of tanδ and Eu increases systematically whereas; systematic decrease in Eg has been observed. It appears that the decrease in the value of Eg and increase in value of Eu leads to an increase in the tunnelling probability of electron from valence band to the conduction band which may result in increase in the value of tanδ. Present investigations strongly suggest that there must be a direct correlation between dissipation factor and electronic disorder term i.e. Urbach energy. Here, a completely new way has been established in order to understand the possible correlation between the dielectric loss, band gap and Urbach energy terms in the form of tunnelling probability. Thus, using the combination of dielectric and optical spectroscopy measurements, a new mechanism has been proposed and demonstrated to understand the origin of dielectric loss in highly correlated electron systems in present work.

The classical ferroelectric material BaTiO3 has been doped with large cation i.e., Hf at Ti site in order to understand the effect of structural disorder in electronic and phononic state. The Raman spectroscopy measurement on these samples indicates increase in the structural disorder with Hf doping. The detail analysis of the Raman spectroscopy data clearly suggests the appearance of new Raman mode at ~ 780 cm−1 and the presence of an asymmetry in almost all Raman modes. The appearance of new Raman mode has been attributed due to the structural disorder induced phonon modes; and this is further confirmed using laser irradiation studies. Additionally, it has been observed that the intensity of this new phonon mode increases systematically with Hf doping; indicating increase in the phononic disorder. It has been observed that the line shape Raman phonon modes show significant asymmetry and this asymmetry along with the full peak width at half maxima (FWHM) of Raman phonon mode shows systematic variation with Hf doping. The observed asymmetric Raman line profile has been analysed through Fano model of electron–phonon coupling which suggests an increase in the electron–phonon coupling with Hf doping. In order to get further insight on increase in the electron–phonon coupling near band edge optical absorption spectroscopy measurements has been carried out and value of electronic disorder in the form of Urbach energy has been estimated and the same is observed to scale with Hf doping. Thus, the systematic increase in the intensity of disorder phonon mode and that of electronic disorder has been observed. This suggests that structural disorder not only affects phonons but electronic state of the system as well. Thus, it appears that the increase in the width of electronic and phononic disorder may overlap in energy scale and may be responsible for the observed increase in the electron–phonon coupling parameter as estimated through Fano equation.

Effect of Hf doping at Ti site in BaTiO3 on the optical band gap (Eg), Urbach energy (Eu), dielectric constant (e) and dielectric loss i.e. loss tangent (tanδ) have been investigated. It has been observed that with Hf doping, the value of Eg and Eu systematically increases whereas; the value of dielectric constant and dielectric loss systematically decreases. The decrease in the value of dielectric constant has been explained in terms of reduction in the tetragonality i.e. by c/a ratio. In the present investigation, it has been proposed that increase in the value of Eg and Eu, leads to decrease in the tunneling probability of electron from valence band to the conduction band which may result in decrease in the value of the dielectric loss. Present investigations clearly suggest that the value of dielectric loss is effectively controlled by Eg. Thus, through present studies, a new methodology has been proposed for understanding the origin of dielectric loss. Moreover, a possible correlation between the Eg and tanδ in terms of tunneling probability has been provided.

Here, we report the possible origin of natural and magnetic field induced polar order near room temperature (RT) in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_{3}$. The temperature-dependent Raman spectroscopy (RS) and synchrotron x-ray diffraction experiments disregard any change in the structure at low temperatures, which is not compatible with the emergence of natural ferroelectricity in this sample. Further, inelastic neutron scattering, neutron Compton scattering, neutron resonance transmission analysis and magnetic field-dependent RS experiments, suggest an increase in the delocalization of ${\mathrm{Pr}}^{3+}$ ions in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_{3}$ with respect to the parent compound $\mathrm{PrFe}{\mathrm{O}}_{3}$. The evaluation of the present results reveals that more delocalized ${\mathrm{Pr}}^{3+}$ ions and strong spin-phonon coupling in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_{3}$ seem to be a driving force for the observed natural and magnetic field induced switchable polar order in $\mathrm{Pr}{\mathrm{Fe}}_{1/2}{\mathrm{Cr}}_{1/2}{\mathrm{O}}_{3}$. The present results provide a significant contribution in understanding the ferroelectric polarization and progress in the search for RT magnetodielectric materials.

We have investigated magnetic, structural and dielectric properties of Bi

Environmentally benign $(1\text{\ensuremath{-}}x)\mathrm{Ba}({\mathrm{Ti}}_{0.8}{\mathrm{Zr}}_{0.2}){\mathrm{O}}_{3}\text{\ensuremath{-}}x({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{TiO}}_{3}$ (BZT-BCT) ceramics are promising materials due to their remarkable high piezoresponse [Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009)]. In this Letter, by focusing on local and average structure in combination with macroscopic electromechanical and dielectric measurements we demonstrate the structure property relationship in the tetragonal BZT-BCT ceramic. During high-temperature cubic to tetragonal phase transformation, polar nanoregions are manifested through the spontaneous volume ferroelectrostriction at temperatures below $\ensuremath{\sim}477$ K. Temperature-dependent local structural investigations across the Zr $K$ edge extended x-ray absorption fine-structure spectroscopy reveal an anomalous collaboration between the ${\mathrm{ZrO}}_{6}$ and ${\mathrm{TiO}}_{6}$ octahedra. These octahedra compromise their individuality during polarization development. The presence of domains of submicron size embedded inside the macroscopic ferroelectric regions below ${T}_{m}$, as well as their hierarchical arrangement, is observed by piezoresponse force microscopy. Effects of the existence of the structural/polar heterogeneities below ${T}_{m}$ are observed also when polarizabilities of the poled and unpoled samples are compared; the poled sample is found to be more susceptible to the electric field. In addition, by using electric field dependent x-ray diffraction studies we also show that this ceramic under field exhibits a reduction of tetragonal distortion, which is consistent with earlier reports.

Al occupancy and local structure (bond lengths and bond angles) for monoclinic β-(AlxGa1−x)2O3 alloys, with Al compositions (x) up to 90%, have been determined from Rietveld refinement of x-ray diffraction data. An Al atom preferentially occupies an octahedron (Oh) atomic site in comparison with a tetrahedron (Td) atomic site. However, a sizable number of Td atomic sites, i.e., 20% for Al composition of 5%, remain occupied by Al atoms, which is found to increase sharply with Al composition. The Oh atomic sites are not fully occupied by Al atoms even for the Al composition of 90%. The lattice parameters (bandgap) of the β-(AlxGa1−x)2O3 alloy decrease (increase) linearly with Al composition, but a change in slope of the variation of both lattice parameters and bandgap is observed at around Al composition of 50%. The lattice is found to be distorted for Al compositions more than 50% as indicated by a large change in the bond angles. The lattice distortion is determined to be the origin for the observed change in slope of the variation of both lattice parameters and bandgap for a monoclinic β-(AlxGa1−x)2O3 alloy system. Our results provide an insight into the local structure of β-(AlxGa1−x)2O3 alloys, which are required to have better understanding of their physical properties.

The origin of ferroelectricity in the cubic phase of BaTi

In this work, we have presented a solid-solution of Sm

The changes in the microstructure of 3.5 MeV proton irradiated T91 Ferritic-Martensitic steel samples with dose have been evaluated using detailed X-ray diffraction line profile analysis of the data collected using both laboratory and the synchrotron source. Different line profile analysis techniques like Williamson-Hall, modified Rietveld method and convolutional multiple whole profile fitting have been applied to evaluate the microstructural parameters such as domain size, microstrain, dislocation density and the character of the dislocation from both the data. The coherent domain size decreases and the corresponding microstrain increases at the first dose of irradiation. With further irradiation, these parameters show a slight recovery and eventually tend towards saturation with increasing dose. The dislocation density follows similar trend as the microstrain showing saturation at higher doses of irradiation in both the XRD data. However, a systematic change in the character of the dislocation from screw-type to edge-type could be ascertained only from the data obtained using synchrotron source. The Vickers microhardness of the samples is found to increase continuously with increasing irradiation dose supporting the observed change in the dislocation character from screw-type (glissile) to edge-type (sessile). Both EBSD and TEM analysis of the unirradiated and irradiated samples have supported the results obtained from the XRD analysis.

The major challenges faced by candidate electrode materials in lithium-ion batteries (LIBs) include their low electronic and ionic conductivities. 2D van der Waals materials with good electronic conductivity and weak interlayer interaction have been intensively studied in the electrochemical processes involving ion migrations. In particular, molybdenum ditelluride (MoTe

Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser deposition (PLD). It is observed that the films grown on GGG(111) substrate exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr effect, bulk magnetization and ferromagnetic resonance measurements. Further, the magnetic bubble domains are observed in the films exhibiting PMA. The observations are explained in terms of the growth direction of Ce:YIG films and the interplay of various magnetic anisotropy terms. The observed PMA is found to be tunable with thickness of the film and a remarkable temperature stability of the PMA is observed in all the studied films of Ce:YIG deposited on GGG(111) substrate., Comment: 7 pages, 10 figures

Optical properties of widely used semiconducting oxides namely; TiO2, ZnO and ZrO2 were investigated using diffuse reflectance spectroscopy (DRS). Prior to the optical absorption measurements, the structural purity of these samples was examined using powder x-ray diffraction experiments carried out on Indus-2 synchrotron source. It is observed that all the studied samples are structurally pure. The DRS of all the studied samples show an extra peak much below fundamental band gap. In order to understand the origin of the said low energy peak, the theoretical optical absorption spectra for these samples have been simulated. The simulations were performed using density functional theory, considering, ideal as well as defected systems i.e. by considering vacancy at all possible sites (for TiO2 we have considered the vacancy at Ti site and also at O site taking in to account surface and bulk effects). It is observed that the simulated optical spectra show very similar feature as that of experimental optical absorption for oxygen vacancy. Photoluminescence spectroscopy further supports the presence of defect states in the studied samples. Thus; it appears that the diffuse reflectance spectroscopy is a useful tool to probe the signature of defects present in the sample.

CsPbCl3 nanocrystals (NCs) are known to show low photoluminescence (PL) quantum efficiency compared to CsPbBr3 NCs. In the present work, at 20 K, stimulated emission is observed from CsPbCl3 NCs at low excitation intensity. Efforts are made to understand the optical behavior and structural properties of chemically grown, 5.3 ± 1.1 nm sized CsPbCl3 NCs. Bulk CsPbCl3 is known to become cubic at 320 K, while, NCs are cubic or tetragonal at room temperature. Temperature dependent PL studies on CsPbCl3 NCs are carried out in a wide temperature range. The primary experimental finding is, about 90 times rise in PL emission intensity and existence of multiple sharp features at low temperature attributable to free exciton, bound excitons, phonon replica along with the defect related emission and stimulated emission. The optical phonon energy is about 26 meV with coupling constant of 54 meV in ∼5.3 nm sized CsPbCl3 NCs. Structural phase transition in CsPbCl3 NCs at about 200 K is also observed.

Detailed structural analysis of rare-earth orthoferrites RFeO3 (R = La, Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, and Yb) has been reported. Polycrystalline samples of RFeO3 were prepared using the sol-ge...

We report the synthesis of polycrystalline (poly)-SiGe alloy thin films through solid state reaction of Si/Ge multilayer thin films on Si and glass substrates at low temperature of 500 °C. The pristine thin film was deposited using electron beam evaporation with optimized in-situ substrate heating. Our results show the co-existence of amorphous Si (a-Si) phase along with the poly-SiGe phase in the pristine thin film. The a-Si phase was found to subsume into the SiGe phase upon post deposition annealing in the temperature range from 600° to 800 °C. Additionally, dual energy band gaps could be observed in the optical properties of the annealed poly-SiGe thin films. The stoichiometric evolution of the pristine thin film and its subsequent effect on the band gap upon annealing are discussed on the basis of diffusion characteristics of Si in poly-SiGe.

Effect of R site ionic radius on the structural, optical and electronic properties of rare-earth orthoferrites (RFeO 3 ) (where, R = La, Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, and Yb) have been investigated experimentally and theoretically. Synchrotron-based X-ray diffraction studies followed by Rietveld refinement confirmed that the lattice constants, R–O bond length and Fe–O–Fe bond angle increase systematically, whereas the Fe–O bond length (i.e. overlap between O-2p and Fe-3d orbitals) associated with FeO 6 octahedra almost remains constant throughout RFeO 3 series. The energy bandgap (E g ) of all the samples have been measured using optical absorption spectroscopy and the same is found between ~ 1.94 and 1.97 eV, i.e. E g almost remains constant throughout RFeO 3 series. First principle DFT analysis confirmed that the “density of states” near Fermi level in all the studied samples is dominated by O-2p and Fe-3d orbitals. Thus, it appears that the constant value of Fe–O bond length (i.e. Fe-O overlap) associated with FeO 6 octahedra might be responsible for the constant value of band gap in these samples.

We show here that the yttrium is immiscible and precipitates with various sizes in the body centred cubic V$_{0.6}$Ti$_{0.4}$ alloy superconductor. The number and size of the precipitates are found to depend on the amount of yttrium added. Precipitates with various sizes up to 30~$\mu$m are found in the V$_{0.6}$Ti$_{0.4}$ alloy containing 5 at.\% yttrium. The large amount of line disorders generated by the addition of yttrium in this alloy are found to be effective in pinning the magnetic flux lines. While the superconducting transition temperature increases with the increasing amount of yttrium in the V$_{0.6}$Ti$_{0.4}$ alloy, the critical current density is maximum for the alloy containing 2 at. \% yttrium, where it is more than 7.5 times the parent alloy in fields higher than 1~T. We found that the effectiveness of each type of defect in pinning the flux lines is dependent on the temperature and the applied magnetic filed., Comment: 10 pages, 14 figures, 3 tables

This paper presents the magneto-structural study on orthoferrite TmFeO3 and Sm substituted TmFeO3 across spin reorientation transition (SRT) temperature. A strong change in magnetic anisotropy due to the substitution of the Sm3+was observed, which is reflected as a change in spin reorientation transition (SRT) temperature. The SRT temperature of Tm0.5Sm0.5FeO3is found to be around 200–230 K, which is relatively high in comparison to TmFeO3. A sudden decrease in the value of coercivity has been observed in the SRT region for both the sample. The lattice dynamics of TmFeO3 and Tm0.5Sm0.5FeO3were investigated by temperature-dependent x-ray diffraction and Raman spectroscopy. We observed unusual contractions in the lattice parameter at low temperatures due to complex exchange interaction between RE3+ and Fe3+ ions sub-lattice. Anomalous behavior in lattice parameters was observed in the vicinity of SRT, which confirms the system’s spontaneous magnetostriction.The strong anomaly was observed in line width and phonon frequency of Raman modes of around SRT, which established the spin-lattice coupling in TmFeO3 and Tm0.5Sm0.5FeO3 nanoparticles. Observation of spin-lattice coupling utilizing Raman scattering substantiates our magnetic and structural correlation and supports its candidature for magneto-elastic applications.

Type 304 stainless steel is a metastable austenitic stainless steel that undergoes strain induced transformation from austenite to α ′ martensite during deformation at room temperature. Role of prior deformation, by rolling at room temperature and at 200 °C (a temperature at which the strain induced martensitic transformation does not occur), on the subsequent room temperature tensile deformation behaviour of the austenite phase is investigated. The changes in dislocation density of the parent phase and the volume fraction of the martensite formed due to deformation were estimated by X-ray diffraction line profile analysis of data obtained from Beam Line - 12 of the Indus 2 synchrotron. The contrast caused by dislocations in the austenite phase has been addressed using the modified Williamson-Hall method. The character of dislocations changes from screw to edge above a critical equivalent strain of ~0.14. The influence of martensite formation on the increase in dislocation density in the austenite phase is confirmed from XRDLPA. An alternative approach to determine dislocation density is proposed which is independent of elastic constants of the material and is found to correlate well with the values determined by the Williamson-Smallman approach. The results obtained from XRDLPA are corroborated with EBSD analysis. It is also seen that the composite strength of the steel, which has undergone different levels of deformation, is related to the changes in dislocation density of austenite and volume fraction of martensite based on Taylor's equation enabling correlation of structure-property.