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The synergistic effect of decoupled thermoelectric parameters on the enhanced power output of a unicouple TEG.

Our research evaluates an innovative sampling technique for household surveys called “geosampling” which leverages recent advances in geographic information systems, computer vision algorithms, and satellite imagery. We compare geosampling to the random walk method. We conducted two surveys in Uttar Pradesh, India: one using geosampling (1,026 completes) and another using random walk (939 completes). We compare the two sampling techniques along three dimensions: (a) performance indicators—response rates and contact attempts; (b) sample composition; and (c) components of variance. We help researchers understand the survey contexts for which geosampling and random walk are best suited.

The hydrothermally synthesized chain molecular magnets [{Fe(Δ)Fe(Λ)}1-x{Cr(Δ)Cr(Λ)}x(ox)2(phen)2]n (x =0, 0.1, and 0.5) have been investigated using neutron diffraction. The structural analysis rev...

Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature application. In the present work, Al addition was found to be highly beneficial for improving the thermoelectric properties of Ag2Se. In Ag1.95Al0.05Se, a large enhancement in the charge carrier mobility (1127 cm2/V s) is witnessed due to the formation of Se-rich Ag2Se1.02 phase with improved grain connectivity through in situ formed AgAl phase. The synergetic effect of low carrier concentration and enhanced mobility in Al doped samples resulted in a high Seebeck coefficient and high electrical conductivity, leading to a high power factor of 3039 μW/m K2 at 300 K. The figure-of-merit of Ag1.95Al0.05Se was found to be 1.1 at 300 K i.e., 57% higher than for pure Ag2Se. The uni-leg device fabricated using Ag1.95Al0.05Se with electroplated Ni/Ag contacts showed a conversion efficiency of ∼3.2% for a temperature difference of 93 K, i.e., comparable to the best reported value for conventional bismuth telluride.

Ni43Mn47Sn11 and Ni43Mn47Sn10.5B0.5 polycrystalline alloys have been prepared by using arc-melting and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), magnetization measurements and microhardness tests. Temperature dependent XRD measurements shows the evolution of monoclinic martensite phase (P12/m1) from the cubic austenite L21 (Fm-3m) phase. An enhancement (73 K) in the martensite transition temperature from 210 K for Ni43Mn47Sn11 to 283 K for Ni43Mn47Sn10.5B0.5 was observed by DSC measurements, which is attributed to the increase in cell volume on the account of B doping. Microhardness measurements showed that the hardness reduces with B doping in Ni43Mn47Sn11 alloy. The magnetic entropy change evaluated from the magnetization measurements was found to be 14 J/kg-K and 17 J/kg-K for Ni43Mn47Sn11 and Ni43Mn47Sn10.5B0.5 alloys respectively. The effective magnetic refrigeration capacity at a maximum field of 5 T was found to be 94 J/kg for Ni43Mn47Sn11 and 55 J/kg for Ni43Mn47Sn10.5B0.5, suggesting that these alloys have potential for magnetocaloric applications (magnetic refrigeration).

The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (

The thermoelectric performance of p-type SiGe is usually inferior as compared to the n-type SiGe. In this work, we demonstrate that by in-situ creation of coherent TiO2 nanoinclusions and boron rich regions in p-type SiGe, a high figure-of-merit of ∼1.3 is achieved at 1100 K, which is 29% higher than pristine p-type SiGe. Such a composite material (SiGe-TiO2) with improved performance was synthesized through vacuum hot pressing of p-type SiGe and TiB2 nanopowders. The phonon scattering and energy filtering of charge carriers at the TiO2/SiGe coherent interface together resulted in lowering of thermal conductivity and enhancement of the Seebeck coefficient. Modulation doping of boron along with improved densification maintain high electrical conductivity. Such a unique combinations of low thermal conductivity, high Seebeck coefficient, and high electrical conductivity of SiGe-TiO2 composite are responsible for the improvement of the thermoelectric figure-of-merit.

A series of MnxCu1–xFe2O4 (x = 0.5, 0.6, 0.7) nanoferrites were prepared by sol-gel auto combustion method. The XRD patterns revealed cubic spinel structure of ferrite systems. Secondary phases of α-Fe2O3 are found also with the ferrite phase. The lattice parameter and crystallite size are found to be in the range (8.314–8.389A) and (12.1–14.5nm). The secondary phases seem to be influence the structural properties of present ferrite systems. Mossbauer spectra showed that each composition have two sextets and two doublets. Core-shell model was well suited to explain the magnetic behaviour of present ferrite systems. The hyperfine fields at A and B sites are influenced by the cation redistribution and predominantly due to Cu2+ ions in the spinel structure. In the present study results of structural and Mossbauer studies are reported.

Bismuth Telluride (Bi2Te3) nanocrystalline material was synthesized using high energy planetary ball-mill at 600 RPM. The Reitveld refined X-ray diffraction pattern of the powder samples confirms the formation of pure Bi2Te3 phase with the particle size of∼58nm. The effect of sintering temperature on the thermoelectric property of the ball-mill sample was studied by sintering the material at 450°C and 550°C. The thermoelectric properties of the sintered pellets were measured in the temperature range of 30-350°C using various characterization techniques. The samples exhibit maximum power factor value of 3mW/m-K and 2.4mW/m-K for the sintering temperature of 450°C and 550°C, respectively. We achieved maximum figure-of-merit (ZT) of 0.8 at 350°C in case of sample sintered at 450°C which is attributed to the better power factor value in this sample.

The structural, microstructural, magnetic and mechanical properties of LaxFe11.6Si1.4 (x = 1.3, 1.7) alloys prepared by arc melting have been studied. The Rietveld refinement of the X-ray diffraction (XRD) patterns shows that increasing La content leads to increase in secondary phases and decrease in 1:13 phase from 88% to 71%. Thermomagnetic measurements show that there is not much change in the Curie transition, however the thermal hysteresis increases with the increase in La content. Table like magnetocaloric effect was observed from 180 K to 200 K in both the alloys. A magnetic entropy change of 19.73 J/kg-K and 15.24 J/kg-K were observed at a low field change of 1 T in La1.3Fe11.6Si1.4 and La1.7Fe11.6Si1.4 alloy respectively. The magnetic entropy change further increases to 23.48 J/kg-K at 183 K and 19.51 J/kg-K at 180 K under an applied filed change of 7 T and the effective magnetic refrigeration capacity was found to be 672 J/kg and 581 J/kg in La1.3Fe11.6Si1.4 and La1.7Fe11.6Si1.4 alloys respectively at a field change of 7 T. The adiabatic temperature was found to be 1.16 K and 2.45 K under a field change of 1 T and increases to 6.05 K and 8.13 K at an applied field change of 7 T in La1.3Fe11.6Si1.4 and La1.7Fe11.6Si1.4 alloy respectively. Increase in La content leads to increase in the mechanical strength suggesting better machinability, thus making them suitable for viable magnetic refrigeration applications.

Ce and Dy substituted Cobalt ferrites with the chemical composition CoCe x Dy x Fe 2-2 x O 4 ( x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz–10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased.

Two stable nitronyl nitroxide free radicals {R1 = 4′-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R2 = 2-(2′-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac)2 (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal–organic complexes Co(hfac)2(NNPhOMe)2, 1; Co(hfac)2(NNT)2·(H2O), 2; Mn(hfac)2(NNPhOMe)·x(C7H16), 3; and Mn(hfac)2(NNT)2, 4. The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C2/c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P21/c space group in which the N–O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions (J/KB) are derived using isotropic spin Hamiltonian H = −2J∑(SmetalSradical) for the model fitting to the magnetic susceptibility data for 1, 2, 3, and 4. The exchange interaction strengths are found to be −328, −1.25, −248, and −256 K, for the 1, 2, 3, and 4 metal–organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal–radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a more significant fraction {∼0.24 for Mn(II) and ∼0.13 for Co(II)} of delocalized spins from the metal ion is transferred to the coordinated oxygen atom(s) of nitronyl nitroxide.

In this study, we report the effect of Mg-substitution on structural, magnetic and dielectric properties of M-type Sr-Cu hexaferrites (Sr 0.5 Cu 0.5−x Mg x Fe 12 O 19 , x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) prepared by using one step solvent free synthesis technique. Rietveld refinement of X-ray diffraction (XRD) patterns has confirmed the formation of M-type hexaferrite phase. The crystallite size was estimated from XRD lies within the nanometer range. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were also employed to estimate the particle size. TEM micrographs of pure and substituted samples show hexagonal structure with an agglomeration is noticed for x = 0.5. Magnetic interactions were studied by vibrating sample magnetometer (VSM) and Mossbauer spectroscopy technique. VSM results reveal that the values of saturation magnetization ( M S ) increases initially for x = 0.2 Mg-substitution after that decreases drastically from 47.15 emu/g ( x = 0.2) to 1.66 emu/g ( x = 0.5). Similar trend was also observed for remanent magnetization ( M r ) and found to decrease from 17.5 emu/g ( x = 0.2) to 0.3 ( x = 0.5) emu/g. Similarly, the higher value of coercivity ( H C = 1995 Oe) was observed for x = 0.2 sample. Room temperature Mossbauer spectra (MS) were recorded to probe magnetic properties at microscopic level. Five sextets were observed for each sub-lattice. Iron ions were found in Fe 3+ high spin state. The dielectric constant of all samples found to be decreased with increase in the frequency. The dielectric dispersion behaviour was well explained in terms of Maxwell-Wagner polarization in accordance with the Koop's phenomenological theory.

In this study, indium (In3+)-substituted NiCuZn nanostructured ceramic ferrites with a chemical composition of Ni0.5Cu0.25Zn0.25Fe2-xInxO4 (0.0 ≤ x ≤ 0.5) were prepared by chemical synthesis involving sol–gel chemistry. Single phased cubic spinel structure materials were prepared successfully according to X-ray diffraction and transmission electron microscopy analyses. The dielectric properties of the prepared ferrites were measured using an LCR HiTester at temperatures ranging from room temperature to 300 °C at different frequencies from 102 Hz to 5 × 106 Hz. The variations in the dielectric parameters e′ and (tanδ) with temperature demonstrated the frequency- and temperature-dependent characteristics due to electron hopping between the ions. The materials had low dielectric loss values in the high frequency range at all temperatures, which makes them suitable for high frequency microwave applications. A qualitative explanation is provided for the dependences of the dielectric constant and dielectric loss tangent on the frequency, temperature, and composition. Mӧssbauer spectroscopy was employed at room temperature to characterize the magnetic behavior.

The investigation under study deals with the combustion synthesis of nanocrystalline Mg substituted nickel zinc ferrites i.e., MgxNi0.6−xZn0.4Fe2O4 (x = 0.0 to 0.6) using malic acid dihydrazide as a novel fuel and the effect of magnesium substitution on the structural and magnetic properties. The nanocrystalline monophasic nature of “as prepared” MgxNi0.6−xZn0.4Fe2O4 (x = 0.0 to 0.6) has been confirmed from XRD and Raman spectroscopic studies and the crystallite sizes were found to be in the range of 19–25 nm which nearly matches with TEM. The RT and low temperature magnetization studies indicate a continuous decrease in magnetization with increase in Mg substitution. In contrast, the hysteretic behaviour diminished and the emergence of superparamagnetism is observed in all the samples as the Mg content increases. The decrease in MS with increase in Mg concentration is attributed to the replacement of magnetic Ni2+ ions with non-magnetic Mg2+ ions and also to the enhancement of the Y–K angle by cation redistribution. The variation of AC susceptibility with temperature exhibits broad maxima, indicating a distribution of particle sizes in the sample with the existence of single domain and superparamagnetic type domain structures. The susceptibility decreases continuously beyond x = 0.4 until 0.6, and the samples exhibit only superparamagnetism. The AC susceptibility studies also show a decrease in Curie temperature (TC) with an increase in x for MgxNi0.6−xZn0.4Fe2O4 (x = 0.0 to 0.6) resulting from weakening of A–B interaction. The ZFC–FC studies along with the Mossbauer studies were also corroborated by the proposed existence of dominant superparamagnetism with an increase in Mg concentration.

Prussian blue analogues (PBAs) have recently been synthesized in the form of various heterostructures such as core–shell nanoparticles, layered thin films, and nanosized metal/PBAs for their multifunctional properties. However, herein, we report the synthesis of a nanocomposite CoFe Prussian blue analogue (CoFePBA) molecular magnet with a polyvinylidene fluoride (PVDF) polymer. The cyanide (CN) group of CoFePBAs interacts with the CF2 dipole of PVDF to integrate PBAs uniformly into a PVDF matrix. Interestingly, the composite material exhibits a spontaneous polarization which is mainly due to the formation of the β phase of PVDF. However, the value of electric polarization is observed to be higher (∼0.04 μC cm−2) than the spontaneous electric polarization (∼0.02 μC cm−2) of the bare PVDF. The higher value of electric polarization is attributed to the enhanced dipole–dipole interactions between the fluoride atoms of PVDF and the cyanide (–CN–) ligand of CoFePBAs. Inclusion of PVDF in CoFePBAs not only helps in improving ferroelectricity, but also improves the thermal stability of the CoFePBAs (up to ∼158 °C), in contrast to the bare CoFePBAs, which are stable only up to ∼65 °C.

A new salt, 4-aminopyridinium 3-(4-aminopyridinium) succinate tetra hydrate was synthesized from 4-aminopyridine and maleic acid in 2:1 stoichiometric ratio. The salt was characterised using single crystal X-ray diffraction, Raman scattering and DSC/DTA techniques. Intermolecular interactions in the salt investigated through Hirshfeld surfaces and 2D finger plots, showed that the C..H, N..H, O..H and H…H interactions were 15.4%, 2.2%,37.6% and 41.3% respectively. The water molecules occupy around 19.2% of the total volume of the unit cell and also contribute significantly to the stability of the crystal. As the salt crystallizes in a non-centerosymmetric space group, it can exhibit second order non-linear optical properties. MOPAC was used to calculate the hyperpolarizability, it was found to be 3.29378 10−30 esu. A database analysis to compare the bond parameters and the physical properties like hyperpolarizability etc. in 4-aminopyridine and its complexes was undertaken. It was found that, in general, complexation or salt formation leads to higher average polarizability, hyperpolarizability and dipole moment, and our salt also has higher hyperpolarizablilty than that of parent compound 4-aminopyridine.

Presence of Hierarchical length scale defect architecture in hot-pressed Bi2Se3 has resulted into a significantly reduced thermal conductivity value of ∼0.7 W/mK and yielded a maximum figure-of-merit value of ∼0.96 at 370K.

Co-precipitated and 800 °C heat treated Ni-Cu-Zn nanoferrites with chemical formula Ni x Cu 0.1 Zn 0.9- x Fe 2 O 4 ( x =0.5, 0.6, 0.7) were prepared because of their potential use as multilayer chip inductors in electromagnetic applications. Their structural, magnetic properties and phase formation were studied using X-ray diffractometer (XRD), field emission scanning electron microscope (FE–SEM), vibrating sample magnetometer (VSM), Mossbauer spectrometer, thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The XRD patterns confirm the cubic spinel structure of the ferrite phase belonging to Fd3m space group. Lattice parameters and cation distributions were obtained by Rietveld refinement of the XRD patterns. The lattice parameter decreases with increase in Ni 2+ ion concentration. Rietveld analysis indicates that Cu 2+ ions predominantly occupy the B -sites and Ni 2+ ions partly going into B -sites but predominantly into A -sites. An excellent agreement is observed between the experimental lattice parameters and lattice parameters theoretically calculated using this cation redistribution. The inversion parameter (λ) observed for Fe 3+ ions by Mossbauer spectroscopy is different from that of Rietveld analysis. Magnetization and Mossbauer spectroscopic measurements indicate that the ferrite nanoparticles are mostly superparamagnetic. The cation redistribution is supposed to alter the magnetocrystalline anisotropy which in turn affects the magnetic parameters of the present ferrite samples. The reduced magnetization is attributed to core-shell interactions and possible canting of A - and B -shell magnetizations. TGA-DSC studies indicate that ferrite formation in the 800 °C heat treated samples is completed but grain growth increases as the particles are subject to the increased temperature.

Series of Mn-substituted Ni-Zn ferrite compositions were synthesized and characterized using XRD, IR, TEM, and Mossbauer studies. The lattice parameter was found to increase with an increase in Mn substitution. The FTIR spectra of ferrites show two principal absorption bands in the regions 580–630 and 390–420 cm−1. The 57Fe Mossbauer spectra recorded at room temperature were fitted with three sextets corresponding to Fe3+ ions at A and B sites and a superparamagnetic doublet. The saturation magnetization shows an initial increase at lower Mn doping and decreases with a further increase in Mn concentration. The coercivity was found to decrease with Mn substitution.

Nano structured CoCrxFe2-xO4 Ferrites with x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 were prepared through Citrate-gel chemical synthesis. DC electrical resistivity (ρ) of the prepared samples was measured in the temperature range of 200–700 °C using two probe method and room temperature Mossbauer measurements were studied. A decreasing trend ρ with an increase in temperature was observed ensuring the semiconducting nature of the ferrites under test. From the Arrhenius plots (log ρ vs 1000/T), corresponding activation energies for conduction of all the compositions were obtained that show a straight line with two slopes. With an increase in Cr composition, resistivity (ρ) of the ferrite samples was found to increase from 1.4 × 106 Ω-cm to 46.2 × 103 Ω-cm at 300 K. Drift mobility was found to increase with increasing temperature due to a decrease in DC electrical resistivity. Curie temperature (TC) was decreased from 740 K to 641 K and the Activation energy of hopping (ΔE) was increased from 0.075 to 0.222 ev with an increase in Cr composition. This suggests that conduction process in the present Co-Cr nano ferrite system is due to hopping of polarons. The results indicate that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region. The presence of a paramagnetic doublet in Mossbauer spectra of the samples was attributed to the presence of very small sized nanoparticles in the superparamagnetic regime.

Polycrystalline nanoferrites with chemical formula MgxZn1−xFe2O4 (x=0.5, 0.6, 0.7) have been synthesized by co-precipitation technique and then subsequently heated to 800 °C in order to investigate structural, thermal and magnetic properties. The samples are characterized by using XRD, FTIR, TGA-DSC, SQUID and Mossbauer spectroscopy techniques. The synergic effect of heat treatment with substitution of Mg2+, results in random variation of lattice parameter (a) and crystallite size (D). FTIR studies revealed the formation of cubic spinel structure. The broadening at octahedral bands for compositions x=0.6 and 0.7 attributes to distribution of ferrite particles of different sizes in these samples. The characteristic feature of hysteresis loops reflects the nature of ferrite particles in the state of superparamagnetism. The saturation magnetization at room temperature has been reported for composition x=0.7 is 44.03 emu/g. The variation of coercivity is due to variation in magnetic anisotropy which is predominately affected by the exchange interactions arising from the nature of nanoparticles. The blocking temperatures are in the range of 10–30 K and their variation is in the line of change in magnetocrystalline anisotropy but not due to variation in crystallite sizes. The Zeeman splitting at tetrahedral (A) and octahedral (B) sites for composition x=0.6 is expected due to increase in size of core of the nanoparticles/or increasing of magnetocrystalline anisotropy. The range of isomer shift values and quadruple splitting values are evident for the presence of Fe3+ ions and the absence of Fe2+ ions in the present systems. The present ferrite nanoparticles in the superparamagnetic state are the potential candidates for biomedical applications like cancer treatment through hyperthermia. The results are interpreted in terms of cation redistribution presuming exchange coupling energy variation on magnetocrystalline anisotropy.

The requirement of higher thermal conductivity is always beneficial forenergy related technological applications. In this regard, we have synthesized Fe2O3−Al2O3/PVDF nanocomposite films based on transition metal oxides (Fe2O3, Al2O3) and PVDF poly(vinylidenefluoride) which show improved thermal properties compared to Fe2O3/PVDF and Al2O3/PVDF films. The films are synthesized by solution casting method at ∼30-40°C temperature and characterized using x-ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. The x-ray diffraction shows the formation of β phase of PVDF and α phase of Fe2O3 in the Fe2O3/PVDF and Fe2O3−Al2O3/PVDF composite films. The films are found to be stable up to ∼400°C. Interestingly, the thermal conductivity is improved for Fe2O3−Al2O3/PVDF composite (∼0.12 Wm−1K−1) as compared to Fe2O3 /PVDF composite (∼0.07 Wm−1K−1). The higher thermal conductivity is discussed in terms of inclusion of nanometer length scale Al2O3 which lowers the interfacial thermal resistance between Fe2O3 and PVDF.

A magnetic proximity effect has been observed in core–shell structure of molecular magnet, Mn 1.5 [Cr(CN) 6 ]· m H 2 O@Ni 1.5 [Cr(CN) 6 ]· n H 2 O, synthesized using a ferrimagnetic core of Mn 1.5 [Cr(CN) 6 ]·7.5H 2 O surrounded by a ferromagnetic shell of Ni 1.5 [Cr(CN) 6 ]·7.5H 2 O. The values of Curie temperature ( T C ) are found to be of ∼65 and ∼60 K for the bare–core and bare–shell compounds, respectively. However, an enhanced T C (∼70 K) has been observed for the core–shell structure. The proximity effect (due to presence of interface exchange coupling) between core and shell is responsible for the observed enhancement of T C . A neutron depolarization study also confirms finite depolarization below ∼70 K.

An attempt has been made to prepare nanocrystalline nickel substituted lithium ferrites, having chemical composition Li 0.5−0.5 x Ni x Fe 2.5−0.5 x O 4 (where x =0.0–1.0 with a step increment of 0.2) by a citrate-gel auto combustion method. Structural characterization of the synthesized samples was carried out by X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (FESEM). Magnetic measurements were carried out using vibrating sample magnetometer (VSM) and Mossbauer spectroscopy. From these measurements it is observed that Ni 2+ substitution in lithium ferrites has strong influence on magnetic properties. Hysteresis loops indicate that the saturation magnetization values were decreased from 56 emu/gm to 28 emu/gm by increasing the Ni 2+ content in the Li–Ni ferrite samples. This signifies the fact that the lesser magnetic Ni 2+ ions are substituted for the magnetic Fe 3+ ions in the octahedral sub-lattice of the ferrites. Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization measurements under an applied field of 100 Oe and 1000 Oe in the temperature range of 5–375 K were performed on two samples Li 0.1 Ni 0.8 Fe 2.1 O 4 and NiFe 2 O 4 . The magnetization as a function of an applied field 10 T was carried out at two different temperatures 5 K and 310 K. These measurements showed the blocking temperature of the two samples at around 350 K above which the materials show super-paramagnetic behavior where the coercivity and remanence magnetization are almost zero.

A series of NixZn1−xFe2O4 (x = 0.5, 0.6, 0.7) were obtained by co-precipitation technique and followed by sintering at 800 °C. The random variation of bond angles resembles possible cation redistribution in the present series of ferrite samples. The cation distributions estimated from Mossbauer analysis are used to find out the net magnetic moment. The magnetic moment n ′ B estimated from Neel’s sub-lattice model is not consistent with experimental magnetic momet n B . But the magnetic moment ( n B ′ ′ ) estimated from the Yafet–Kittel (Y–K) model is in good agreement with the experimental magnetic moment n B , supporting the possibility of non-collinear arrangement of spins at B–site. The non-collinear spin arrangement at octahedral (B) site is influencing the magnetization of present series ferrite samples. The increase in saturation magnetization with increase in Ni2+ ion concentration is expected due to the decrease in non-collinear spin arrangement at octahedral (B) site. Higher saturation magnetization of 61.32 emu/g was reported for the composition x = 0.7. The single domain structure of samples is evident from the hysteresis loops, but interestingly nature of hyperfine interactions can be found from the Mossbauer spectra under spectral line intensities. The increase in the blocking temperature (magnetic ordering) is due to the increase in magnetocrystalline anisotropy rather than an increase in particle sizes. The composition x = 0.7 is showing good sensor response for both LPG and acetone. Moreover, its response and recovery times are less comparing to the other two compositions and therefore it is useful for the sensor fabrication.

BiFe1-xCoxO3 (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles (NPs), were prepared by ethylene-glycol-based sol-gel technique. Phase purity of the NPs was confirmed by x - ray diffraction (XRD) technique. The average size of pristine BiFeO3 (BFO) NPs was found to be 46 nm, which initially increased to 50 nm for 1% Co doping and then decreases to 48, 45 and 43 nm for 3%, 5% and 7% Co-doped BFO NPs, respectively. X-ray photoelectron spectroscopy (XPS) and Mossbauer spectroscopy confirmed that the oxidation state of Fe and Co is +3. In the low frequency region, the dielectric constant (e‘) shows a maximum decrease by 96% (137 → 5.1) on 5% Co-doping concomitant with 62% decrease in dielectric loss (0.32 → 0.12) which indicates substantial reduction in leakage current density. Further, the pristine BFO shows a well-defined dielectric loss peak at 40 Hz (tan δ = 0.4). In contrast, twin dielectric loss peaks are uniquely observed for all the Co doped BFO NPs. 1% doped NPs show first and second peaks at 7 Hz and 20,400 Hz, respectively, which shifts to higher frequencies of 245 Hz and 154,000 Hz, on 5% doping. The magnetic measurements (M − H) revealed the ferromagnetic behaviour of the NPs. On Co doping, saturation magnetization (Ms) increased with decrease in coercive field (Hc). A maximum enhancement of 226% (0.93 → 3.05 emu/g) in Ms values concomitant with decline of 61% in Hc values (80 → 15 Oe) was observed for 7% doping. The reduction in leakage current and enhancement of magnetic properties makes the NPs better-suited for device applications.

We report the magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy prepared by mechanical alloying followed by spark plasma sintering and annealing the spark plasma sintered alloy. The X-ray diffraction pattern confirms the presence of hexagonal Fe2P-type phase in both (as-prepared and annealed) alloys. Annealing of the spark plasma sintered alloy leads to the increase of the volume fraction of the Fe2P phase from 87% to 98% and a decrease in the lattice volume. Thermo-magnetic measurements show that Curie temperature (TC) decreases from 291 K to 289 K after annealing the spark plasma sintered alloy. Thermal hysteresis reduces from 19 K to 9 K after annealing the spark plasma sintered alloy. The magnetic entropy evaluated from magnetization measurements was found to be 8 J/kg-K in the spark plasma sintered alloy and it increases to 19 J/kg-K in the annealed spark plasma sintered alloy under 3 T magnetic field. The refrigerant capacity of the annealed spark plasma sintered alloy was found to be 200 J/kg at 3 T. The adiabatic temperature change of the annealed alloy has been estimated from the heat capacity measurements and it was found to be 1.9 K at 1 T and increases to around 2.7 K under a magnetic field of 3 T. Annealing the spark plasma sintered alloy leads to decrease in the hardness and it is observed that both the alloys crack after thermal cycling. However, the large change in magnetic entropy and adiabatic temperature change very near to the room temperature makes Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 alloy a promising magnetocaloric material.

Mg substituted X–type hexagonal ferrites with the chemical composition Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were successfully synthesised by a sol–gel auto–combustion technique, in order to investigate the effect of Mg substitution on structural, magnetic and dielectric properties. XRD analysis of prepared samples revealed the formation of pure X–type phase. The variations (decreasing trend) in lattice parameters with Mg substitution indicate the incorporation of Mg substitution into the crystal structure. The average crystallite size of heated powders was found to be in the range of 16–22 nm. For the first time, the RT hysteresis loops of Ba2Zn2Fe28O46 (Zn2X), Ba2Mg2Fe28O46 (Mg2X) and Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were measured. The saturation magnetisation showed an initial decrease with x = 0.4 − 1.2, and then an increase with x > 1.2, to the largest final values of 63.29 A m2 kg−1 for the fully Mg–substituted x = 2.0. The value of coercivity lies in the range of 89.9–209.3 kA m−1 (1130–2630 Oe), and the magnetic results suggest that the compositions x = 0.0, 0.4 and 1.2 possess multi-domain microstructures, while x = 0.8, 1.6 and 2.0 possess single domain microstructures. The room temperature Mӧssbauer spectra were analysed with six sextets of five magnetic sublattices, and the results are presented as a function of Mg substitution. It was found that initial levels of Mg substitution reduce the Fe populations at a and b (spin up) sublattices, but that with x > 1.2 these become repopulated at fIV (spin down) site, resulting in an increase in magnetisation. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and results show normal behaviour for ferrimagnetic materials. At low frequencies (100 Hz–2 MHz), relative permittivity was constant between 0.3 and 1.5 above 20 kHz, with the higher values belonging to the more dense samples. All Mg substituted samples had lower losses above 20 kHz than the pure Zn2X. In complex measurements at microwave frequencies (500 MHz–13.5 GHz), all samples had a real permittivity of around 7.5, except for the fully Mg–substituted sample (x = 2.0), which had a lower e′ of 5.5. For two samples (x = 0.4 and 1.6) we observed dielectric resonances between 12.85 and 13.25 GHz. All showed a steady real permeability of around 1.2–1.5 over the whole 1–13 GHz range, and ferromagnetic resonance (FMR) between 1 and 5 GHz, and ∼12.5 GHz.

The one–dimensional (1-D) single chain molecular magnet [{FeII(Δ)FeII(Λ)}0.5{CrII(Δ)CrII(Λ)}0.5(ox)2(phen)2] is hydrothermally synthesized using oxalate (ox) and phenanthroline (phen) ligands with transition metal ions (Fe and Cr). The compound is characterized using x-ray diffraction, dc magnetization measurements and P-E ferroelectric loop measurements. The diffraction analysis using Rietveld refinement confirms a single phase formation of the compound in monoclinic structure with space group of P21. The compound crystallizes in 1-D chain like structure containing two different crystallographic sites of metal ions (Δ– and Λ−), which are bridged by the ox ligand and Phen ligand. These two metals site are different in bond length and bond angles results lattice distortions. The lattice distortion induces ferroelectric behavior in the compound which is discussed in terms of lattice distortion induced dipole moments.The one–dimensional (1-D) single chain molecular magnet [{FeII(Δ)FeII(Λ)}0.5{CrII(Δ)CrII(Λ)}0.5(ox)2(phen)2] is hydrothermally synthesized using oxalate (ox) and phenanthroline (phen) ligands with transition metal ions (Fe and Cr). The compound is characterized using x-ray diffraction, dc magnetization measurements and P-E ferroelectric loop measurements. The diffraction analysis using Rietveld refinement confirms a single phase formation of the compound in monoclinic structure with space group of P21. The compound crystallizes in 1-D chain like structure containing two different crystallographic sites of metal ions (Δ– and Λ−), which are bridged by the ox ligand and Phen ligand. These two metals site are different in bond length and bond angles results lattice distortions. The lattice distortion induces ferroelectric behavior in the compound which is discussed in terms of lattice distortion induced dipole moments.

The nanocrystalline Co1−xMnxFe2O4 (0 ≤ x ≤ 0.5) ferrites are synthesized by auto-combustion method. The structural properties and phase identification of the samples are studied using X-ray powder diffraction and the Rietveld analysis. The refinement results confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice is partially inverse. The magnetic properties of the prepared samples are studied by using an M–H hysteresis curves. The maximum saturation magnetization and coercivity of samples are 68.94 emu/gm and 1.59 KOe respectively. From 57Fe Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Mn2+ substitution have been studied. The composition dependent cation distribution estimated from Rietveld analysis and magnetic studies is in good agreement with each other.

Nano structured indium substituted NiCuZu ferrites with chemical composition Ni05Cu0.25Zn0.25 Fe2-xInxO4 (0.0

Spray drying had been used to synthesize silica-carbon black nanocomposite micrometric granules with a uniform distribution of the two components. This was achieved by hindering the preferential diffusion of hydrophobic carbon and hydrophilic silica particles in the water droplets during evaporative assembly by introducing gum arabic as a stabilizing agent and network former. Both positive and negatively charged silica nanoparticles were used to check the stability of the sol and its effect on the morphology of the spray dried granules. X-ray and neutron scattering, complemented with electron microscopy, were used to investigate the correlation and distribution of the nanoparticles within the granules. Porous silica granules, having surface area of 157 m2/g, were obtained after removal of carbon black by calcination. An environment-friendly solar absorbing coating had been prepared using as synthesized granules.

Ti-Ni alloy thin films are prepared using ion beam sputtering at different Ar gas flow rate, and corresponding structural and electronic properties are investigated. The films are characterized by using grazing incidence X-ray reflectivity) and x-ray diffraction techniques in order to determine the structural changes with the argon (Ar) flow rate. The diffraction measurement confirms amorphous nature of all deposited thin films. The recorded core level spectra of Ti and Ni-2p also show shift in their binding energy to higher side with respect to pure element form, confirming Ti-Ni alloy phase formation at room temperatures. The Ti and Ni atomic concentration values obtained from fitted core-level spectra are found to decrease with higher Ar flow rate. In addition to this, valence band spectra also show changes in Ni-3d density of states with Ar gas flow rate. The results are interpreted and discussed in terms of structural change with Ar flow rate.

In the present work, we report on the investigation of low-temperature (300-5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10(-7) obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α(2)σ).

Nanopowders of Mn x Zn 1− x Fe 2 O 4 with x =0.4, 0.5 and 0.6 were synthesized using a combustion synthesis method. X-ray diffraction (XRD) patterns obtained on samples confirmed formation of monophasic cubic phase material. Lattice parameters and X-ray densities were obtained from rietvield refinement of the XRD patterns. All samples were radiated with gamma radiation with a dose of 200 Gy obtained from 60 Co source. Structural and physical parameters, such as lattice constant, X-ray density and particle size, determined for as prepared samples ( S A ) and gamma irradiated samples ( S R ), showed extraordinary variations in their values. Saturation magnetizations (M S ), remnant magnetization (M R ) and coercive field (H C ) for both sets of samples illustrated an enhancement in their values for S R samples. Investigations were carried out using Mossbauer spectroscopy to divulge structural and magnetic information of all samples. Room temperature Mossbauer spectra were fitted with five magnetic sextets and a symmetric paramagnetic doublet for the data obtained on samples except for x =0.4, S A sample. The presence of well defined doublets in the spectra of S A and S R samples is attributes of superparamagnetism, indicating the reduction in A–B superexchange interaction due to dilution of sub-lattice by Zn ions. Cation distribution at A site and B site, estimated from Mossbauer data exhibited amazing alterations which were highly stable. The variations in physical, structural and magnetic properties observed are attributed to change of Fe 2+ /Fe 3+ and Mn +2 /Mn +3 ratios in gamma-irradiated samples.

The Cr3+ ions doped multi-oxide ZnFe2−xCrxO4 ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn2+, Cr3+ and Fe3+ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr3+ content in place of Fe3+ ions at octahedral B-site. Typical blocking temperature (TB) around 90 K was observed by zero field cooling and field cooling magnetization study. Room temperature Mossbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr3+ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe2+ and Fe3+ ions with a thermal activation.