Search

We have investigated the structural, magneto-resistive, electrical, and thermal transport properties of monovalent substituted polycrystalline Nd0.7Sr0.3−xAxMnO3 (x = 0, 0.1 and A = Na, Ag, K) compounds. The Rietveld refinement of the X-ray diffraction patterns reveals that all samples crystallize in orthorhombic structure with Pnma space group. The scanning electron microscopy micrographs evidenced that the grains acquire uniform morphology, nearly spherical, and unequal grains in all the studied samples. The decrease in metal-insulator transition temperature on the monovalent substitution is a result of reduced double-exchange interactions. Further, above the metal-insulator transition, electrical transport properties are analyzed through variable range hopping and small polaron hopping models. The substitution of monovalent cations enhanced the experimental parameters like hopping distance and activation energy, while the density of state at the Fermi level decreased significantly. On the monovalent doping, the samples showed very high magnetoresistance (MR%), and the temperature coefficient of resistance (TCR%) makes them prospective candidates for advanced uncooled infrared bolometers. The thermoelectric power (S) demonstrates a positive to a negative crossover, and the value of S increased in doped samples. At the higher temperatures, the small polaron is responsible for the conduction process.

Structural and magnetic behavior of a series of new cobaltite Y1-xYbxBaCo4O7 (0 ≤ x ≤ 0.5), prepared using the conventional solid state reaction method have been investigated. Increasing Yb...

The environment and the health of the masses are being affected by toxic gases such as O3, SO3, CH2O, H2S and HCN. In this study, we investigate the interaction of such toxic gases on SnS monolayer using density functional theory (DFT). The interaction between species and adsorbent is explained on the basis of their adsorption energy, electronic properties and charge transfer. Our results demonstrate that the process of adsorption of O3 and SO3 is chemisorbed in nature whereas CH2O, H2S and HCN is physisorbed. The validity of the adsorption process is further confirmed within the frame of electronic properties and charge transfer. As a result, we find each of the investigated gas molecules is acting as a charge acceptor. Diversity in the adsorption of customary gas molecules on the SnS monolayer gives rise to a possibility to exploit them as chemical gas sensors.

In the present density functional theory based study, we have investigated the interfacial electronic properties and adsorption curve along with chemical bonding with interface of MoS2/SrO. Our calculations indicates that the electronic properties are highly interface dependent as the heterostructure (HS) shows metallic behavior in MoS2/SrO interface. The equilibrium interlayer distance deq between MoS2 and SrTiO3 (STO) is found within 2.62 to 2.67 . From our adsorption curve analysis, we have found that MoS2 is chemisorbed over STO substrate. Chemical bonds at the interface shows ionic bonding in MoS2/SrO interface. A unique behavior of cubic confined MoS2 monolayer is also observed in our investigation i.e. an indirect band gap of ∼1.63 eV is found. This behavior may lead to fabricate and investigate Si in the form of hexagonal honeycomb like monolayer which could present a direct band gap. Conclusively we can use the above investigated HS in metallic applications.

This report presents the structural, magnetoresistance, electrical and thermal transport properties of Aluminium substituted La 0.7 Ba 0.3 Mn 1−x Al x O 3 (0 ≤ x ≤ 0.15) compounds synthesized by solid state reaction method. To obtain crystallographic parameters, the X-ray diffraction patterns are fitted in R-3c space group with Rietveld refinement method. The resistivity and magneto-transport measurements are performed using standard four-probe assembly with and without magnetic fields. The peak resistivity ρ peak is noted at Metal-Insulator Transition temperature ( T MI ) and lowering in T MI is observed for higher concentrations of Al 3+ . The resistivity data have been analyzed in two parts. Firstly, in the metallic region below T MI the resistivity data is fitted with three degree polynomial. Secondly, in the semiconducting region above T MI data have been fitted with Variable Range Hopping (VRH) and Small Polaron Hopping (SPH) models. The Seebeck coefficients found to be positive throughout the temperature range (10 K–300 K) with holes as dominating charge carriers. Similar to the resistivity profile, in metallic region the thermo-power is explained with qualitative model based on diffusion, magnon-drag, phonon-drag and spin fluctuation contributions whereas the semiconducting region is explained with small polaron hopping model.

In the present paper we have studied the effect of Sm doping on the magnetic and magnetocaloric properties of La 0.7-x Sm x Ba 0.3 MnO 3 (0 ≤ x ≤ 0.2) compounds. These sample have been synthesized by conventional solid state reaction method. The analysis of synthesized samples by X-ray diffraction showed that the formation of single phase compositions and doping of La 3+ by Sm 3+ ion converted the chemical structure form rhombohedral ( R-3C ) to orthorhombic ( Imma ). The magnetic study measurement specified that the ferromagnetic double exchange interaction is weakened with increasing Sm content as a consequence of the curie temperature (T c ) shift in lower temperature from 340 K for x = 0, 290 K for x = 0.1 and 225 K for x = 0.2 compounds. Using the Banerjee’s criterion plots, it is found that the phase transition for all samples in the second-order. All reported compounds exhibit a maximum and large magneto-caloric effect near the Curie temperature (T c ). The magnitude of the maximum magnetic entropy change is found to be decrease with increasing of Sm doping content i.e. 4.39 J/kg K for x = 0, 4.22 J/kg K for x = 0.1 and 2.48 J/kg K for x = 0.2 in applied field change of 5T. The trend of large entropy change and the convenient adjustment of the Curie temperature make these oxides useful for magnetic refrigeration in an extended high and low temperature even at near room temperature.

In the present paper we studied the structural, magnetotransport and thermopower properties of a series of polycrystalline La 0.7−x Sm x Ba 0.3 MnO 3 (0≤x≤0.2) compounds which were synthesized by conventional solid state reaction techniques. The Rietveld refinement of the X-ray diffraction pattern predicts the formation of single-phase compositions and doping of La 3+ by Sm 3+ ion converted the chemical structure form rhombohedral ( R-3C ) to orthorhombic ( Imma ) The scanning electron microscopy show clean smooth and densified structure images be a sign of good crystalline nature of the samples. The temperature dependent electrical resistivity is measured by standard four-probe method between 5 and 300 K exhibits Metal–Insulator Transition MIT which shows the decreasing trend with increasing Sm doping content and metallic state (T p2 ) that signifies importance of electron-electron, electron–phonon and electron-spin fluctuation scattering process. The metal–insulator transition temperature (T p2 ) is observed which decreases with the increase in doping content when magnetic field is applied. The resistivity data in high temperature region (T>T p2 ) are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The application of magnetic field suppresses the resistivity in entire temperature range and with increasing the Sm 3+ content the samples showed very high magnetoresistance. The thermoelectric power (S) of the reported samples exhibit a crossover from positive to negative value and it increases in doped samples. The analysis of thermoelectric power data confirms the applicability of the small polaron hopping model in high temperature region and in low temperature fitted to an equation containing diffusion, magnon drag, phonon drag and electron-spin fluctuation term. An appropriate justification for the observed behavior is specified.

We have synthesized a series of Sm 0.55 Sr 0.45−x Ag x MnO 3 (x = 0 & 0.15) by conventional solid state reaction method to scrutinize the effect of monovalent Ag + as a replacement of Sr 2+ ion on structural, electrical, magnetotransport and thermoelectric properties. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure having orthorhombic ( Pnma ) symmetry without any detectable impurity phase. It is observed that M ZFC and M FC curves become more manifested as Ag + content is increased which indicates an increase in magnetic frustration arising due to bending of Mn-O-Mn bond. The M-H plots show the narrow hysteresis loops which indicate the soft ferromagnetic nature. Magnetic studies also show that the Curie temperature T C is found to decrease with Ag + content. The metal–insulator transition temperature (T MI ) is observed which decreases with the increase of Ag + content when magnetic field is applied. The resistivity data in high temperature region are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The thermoelectric power (S) of the reported samples exhibits a crossover from positive to negative value and value of S increases in doped samples. The analysis of thermoelectric power data confirms that the small polaron hopping model in high temperature region and at low temperature electron–magnon scattering is the dominating in the FM region. With increasing the Ag + content the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR%) which make the compound more promising for scientific and technological applications.

The perovskite manganites compounds with nominal composition YMn 1-x Ru x O 3 (YMRO) ( x = 0, 0.05, 0.1 and 0.2) were investigated systematically through structural, morphology and thermal transport measurements. Our thermopower and specific heat measurements indicate that the ground state of rare earth manganite compounds is highly sensitive to the ruthenium (Ru) concentration at Mn-site and henceforth to its cationic radius. These properties were analyzed by considering various models and empirical relations. The high value and complicated temperature dependence of thermopower (S) is an indication of electron–magnon scattering in these systems. The observation of giant suppression in the S with increasing Ruthenium content confirms the mixed-valence subsistence of Mn - Ru network. Specific heat measurements depict an anomaly in the vicinity of T N and associated entropy change, was then obtained by subtracting the lattice part from the experimental data, indicating the existence of magnetic ordering and magnetic inhomogeneity in the samples.

Silver ions substituted samarium strontium manganite (Sm0.55Sr0.30Ag0.15MnO3) pervoskite was synthesized by using respective oxides in stoichiometric ratio through solid state reaction. The as-prepared sample was characterized by various analytical techniques to confirm its formation and understand the effect of monovalent silver ions in pervoskite lattice. X-ray diffraction pattern confirms the single phase formation while grain morphology in SEM image indicates good connectivity among the grains. The enhancement in metal to insulator transition temperature shows quenched disorder and magnetoresistance phenomena. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) emerge from grain growth factor and homogeneity induced by Ag+ ions in the lattice. The reduction in hysteresis loss resulted from antiferromagnetic - ferromagnetic (TN) and ferromagnetic - paramagnetic (Tc) transitions reveals the removal of disorder in perovskite lattice by Ag+ ions substitution. This increases the magnetic moment across distinct ions on the applying magnetic field. The rise in MR% (~99%) with silver doping emerging from smooth spin tunneling of the grains across the boundary and suppression of the disordered magnetic fluctuations with increase in magnetic field has been reported. The present compound exhibits the first order nature of magnetism and observed first time the highest value of TCR ~ 95%.

Polycrystalline yttrium barium cobaltite (YBaCo4O7) powdered sample was prepared by conventional solid state reaction route using high purity yttrium oxide, barium carbonate and cobalt oxide. The as-prepared sample was characterized by XRD diffraction, SEM/EDAX, Raman analytical techniques, resistivity and magnetization measurements for structural, morphological, electrical and magnetic properties assessment. XRD pattern confirms the single phase formation of the sample without any impurity. SEM image shows the hexagonal growth of the crystal and EDAX spectrum reveals stoichiometric composition of as prepared sample. The variation in electrical resistivity from 90 K to 300 K follows the variable range hopping conductivity mechanism. The strong broad overlapped Raman peaks of Co–O and Y–O stretching and bending vibrations of tetrahedral CoO4 with included components of YO6 of octahedral symmetry are obtained at 542 cm−1, 486 cm−1 and 636 cm−1, 436 cm−1, respectively. DC magnetic susceptibility exhibits very weak ferromagnetism below 80 K and does not obey Curie-Weiss law.

The polycrystalline samples with nominal composition Eu0.5Sr0.5Mn1−x Cr x O3 (0 ≤ x ≤ 0.1) were prepared by the conventional solid state reaction method and characterized by X-ray diffraction, scanning electron microscopy and electrical resistivity behavior without and with magnetic field. The structural parameters obtained by using Rietveld refinement of X-ray diffraction data showed that all samples crystallize with orthorhombic perovskite type symmetry with Pbnm space group. The scanning electron micrograph images reveal that the increase in Cr substitution hinders grain growth and grain connectivity. The temperature dependence of electrical resistivity show the semiconducting nature of these compounds and support the small polaron hoping model and variable range hopping conduction model. The calculated hopping distance and activation energy decreased as rate of Cr content increased whereas density of states at Fermi level increased. A large negative magnetoresistance is also present in the sample at the lowest temperature of measurements.

We have investigated the thermodynamic properties of Ln1−xSrxCoO3 (Ln = Pr, Nd, Sm, Dy and 0 ≤ x ≤ 1) perovskites using modified rigid ion model (MRIM) and a novel atomistic approach of Atoms in Molecules (AIM) theory. The effect of Sr doping on lattice specific heat and thermal expansion coefficient as a function of temperature (1 K ≤ T ≤ 300 K) are reported probably for the first time. The MRIM results on thermal expansion coefficient of Sr doped LnCoO3 (Ln = Pr, Nd, Sm and Dy) suggest that higher Sr doping may not be applicable to solid oxide fuel cell. Besides, we have reported bulk modulus (B), cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD), Gruneisen parameter (γ) and specific heat. It is found that the present model has a promise to predict the thermodynamic properties of other perovskites as well.

We have synthesized the single phase polycrystalline sample of silver doped disordered Sm0.55Sr0.45−xAgxMnO3 using the conventional solid state method. They have been investigated by X-ray diffraction for phase evolution and their Rietveld refined X-ray diffraction pattern indicates an increase in lattice parameters and unit cell volume with Ag doping. The magnetization analysis shows the presence of a first order paramagnetic to ferromagnetic transition; the transition temperature and amount of thermal hysteresis decreases on Ag doping. The transport, magneto-transport results indicates decrease in metal to insulator transition, drastic increase in resistance and temperature coefficient of resistance (TCR %) with nearly unaffected colossal magnetoresistance effect which indicates that at least a part of silver is incorporated in the lattice. Scanning electron micrographs indicate that silver has also increased the grain growth sharpness and thus decrease the effect of grain boundary scattering. The significant value of TCR of ∼43% of our samples indicates their applied nature for bolometric application.

The Single phase Ho1-xGdxMnO3 (0 ≤ x ≤ 0.1) compounds were synthesized by solid-state reaction techniques and characterized with various techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, ferroelectric loop tracer. The Rietveld refined X-ray diffraction and Raman patterns indicate that all the compounds exhibit a single-phase hexagonal structure with a P63cm space group. The room temperature Raman spectra signify that the phonon peaks observed in all reported samples, slightly shift towards the lower temperatures. Moreover, an increase in the polarization values and reduction of leaky nature with increment in Gd concentration has been observed. The improved ferroelectric parameter obtained in our study is an advancement in the present understanding of multiferroic compounds.

The brownmillerite structure of a technologically important oxide Ca2Fe2O5 (CFO) consists of alternating layers of octahedra and tetrahedra of Fe and O, with the tetrahedral layers having intrinsic O vacancies. In this work, using first principles density functional theory based calculations, we have studied the stability, structure and electronic properties of the polar (0 1 0) surface of CFO. In contrast with those observed in case of the polar surfaces of conventional perovskites, we find that the stoichiometric, unreconstructed, Fe containing terminations are more stable than the non-stoichiometric reconstructed ones. In particular, our calculations show that depending on temperature and oxygen partial pressure, there are two possible stable terminations: (a) the layer containing the Fe and O atoms in the octahedron and (b) the layer containing the Fe and O atoms in the tetrahedron. While the former is metallic, the later has a band gap. The unreconstructed terminations are stabilized by dipole compensation through charge rearrangement in the surface layers during structural relaxations.

In the present study, we select the toxic gases such as NO2, NO, SO2, NH3, CO and CO2 to examine the sensing capacity of S-vacancy SnS monolayer as a gas sensor. The selectivity towards a gas by a sensing device is investigated in terms of adsorption energy, charge transfer and electronic properties of the most stable geometries of the adsorbed system. Comparison of the adsorption behavior of species on the pristine and defective ML, reveals that defective monolayer is more sensitive towards SO2, NO and NO2 molecules with the chemisorption process. The density of states show the adsorption of NO and NO2 significantly modify the electronic properties of the SV-SnS ML, but the strong adsorption creates difficulty in desorption process and shows unrealistic use as a gas sensor at room temperature. At the same time, due to the desirable adsorption energy of SO2 and short recovery time, SV-SnS ML can be a promising gas sensing material for SO2 gas detection. The present findings demonstrate SV-SnS ML, could be used as a potential material for gas absorbent and sensing applications.

A series of GdMn1−xCrxO3 (0 ⩽ x ⩽ 0.2) have been synthesized by the conventional solid state reaction method mainly to understand the response of Cr substitution on structural, microstructural, magnetic and electrical transport properties. The X-ray diffraction shows that all samples crystallize with orthorhombic perovskite type symmetry with Pbnm space group. The room temperature Raman spectroscopy shows the reduction of Raman shift as doping concentration increase that related to anti-symmetric Jahn Teller stretching mode and symmetric-stretching mode. The temperature dependence of electrical resistivity show the semiconducting nature of these compounds and support the small polaron hoping model (SPH) and variable range hopping conduction model (VRH). The calculated hopping distance and activation energy increased as rate of Cr content increased whereas density of state at Fermi level decreased. The temperature dependence of magnetization presents that under the zero field cooling (ZFC) mode as doping concentration increases the net magnetization reverses its nature below irreversibility temperature. The magnetization results show that all samples show weak ferromagnetic nature that can further be improved with increasing Cr ions concentration.

We have investigated the bulk modulus and thermal properties of proton conducting perovskite RCeO 3 ( R = Ba, Sr) for the first time by incorporating the effect of lattice distortion in modified rigid ion models (MRIM). The computed bulk modulus, specific heat, thermal expansion coefficient and other thermal properties of BaCeO 3 and SrCeO 3 reproduce well with the available experimental data. In addition the cohesive energy ( ϕ ), molecular force constant ( f ), reststrahlen frequency ( ν ), Debye temperature ( θ D ) and Gruneisen parameter ( γ ) are also reported and discussed. The specific heat results can further be improved by taking into account the spin and the orbital ordering contribution in the specific heat formulae.

We have synthesized Pr0.67Sr0.33−xAgxMnO3 (0 ≤ x ≤ 0.1) compound by conventional solid state reaction method at different sintering temperature. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure with orthorhombic (Pnma) symmetry without any detectable impurity phase. The grain growth and grain connectivity extensively improved at higher sintering temperature with doping concentration. Depending upon the doping and the increment of sintering temperature, the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR). An improvement in magneto-resistance and TCR with increasing the sintering temperature i.e., 1200–1300 °C which make the compound more promising for scientific and technological applications.

We have investigated the various lattice distortions in complex oxides Ca1-xLaxMnO3 and its effect on elastic and thermal properties of these perovskite manganites, especially Debye temperature of these complex oxides. The revealed data on Bulk modulus and Debye temperature studied as a function of lattice distortions using a novel atomistic approach of Atom in Molecules(AIM) theory and Modified Rigid Ion Model (MRIM) are in closer agreement with the available experimental data for some concentrations (x) of Ca1-xLaxMnO3. We demonstrate that the distortions introduced due to electron concentration, size mismatch and JT effects are the dominant factor, whereas charge mismatch and buckling of Mn-O-Mn angle influence the thermal properties to a lesser degree in the ferromagnetic state.

Ab-initio calculations are carried out to study the electronic and chemical bonding properties of Intermetallic full Heusler compound Pd2HfIn which crystallizes in F-43m structure. All calculations are performed by using density functional theory (DFT) based code Quantum Espresso. Generalized gradient approximations (GGA) of Perdew– Burke– Ernzerhof (PBE) have been adopted for exchange-correlation potential. Calculated electronic band structure reveals the metallic character of the compound. From partial density of states (PDoS), we found the presence of relatively high intensity electronic states of 4d-Pd atom at Fermi level. We have found a pseudo-gap just abouve the Fermi level and N(E) at Fermi level is observed to be 0.8 states/eV, these finding indicates the existence of superconducting character in Pd2HfIn.

We have synthesized and investigated the effect of Ag doping in Pr0.67Sr1−xAgxMnO3 (0≤x≤0.3) perovskite materials via solid state reaction route. The structural, transport and magnetoresistance behavior have been studied. The Rietveld refinement of X-ray diffraction data shows that the compounds crystallize in an orthorhombic structure with Pnma space group with systematic non-linear variation in unit cell volume and lattice parameters. The grain morphology confirms that silver enhances conducting channels and reacts well with the compound only upto a certain doping level. The temperature dependent zero-field and in-field resistivity have been measured between 5 K and 300 K. The samples exhibit a systematic variation in metal to insulator transition temperature and a large magnetoresistance at x=0.10. The highest value of temperature coefficient of resistance has been observed by us for the first time. The results revealed that Ag takes part in the reaction only when the doping amount is small and at higher doping the system becomes a two phase composite.

The elastic and thermal properties of highly Sr-doped Ln0.05Sr0.95CoO3−δ (Ln = Sm, Gd, Dy, Y, Ho, Er, Tm and Yb) in cubic phase have been investigated probably for the first time by using modified rigid ion model (MRIM). The computed results on the second order elastic constants (C11, C12 and C44) and their combinations are reported and discussed. The calculated elastic constants indicated that Ln0.05Sr0.95CoO3−δ are mechanically stable. Besides, we have reported the cohesive, thermal properties and the variations of specific heat with temperature are discussed in detail.

We have investigated the specific heat of hole-doped vanadium oxides Y 1− x Ca x VO 3 (0 ≤ x ≤ 0.11), Pr 1− x Ca x VO 3 (0 ≤ x ≤ 0.3) and Nd 1− x Sr x VO 3 (0 ≤ x ≤ 0.2) probably for the first time by applying the Modified Rigid ion model (MRIM). The results obtained on temperature dependent (1 K ≤ T ≤ 300 K) specific heat are in reasonably good agreement with the experimental data. The impact of lattice distortions on the elastic and thermal properties of the present Mott insulators is portrayed by an atomistic approach. The scope of further improvement in the present model has also been discussed.

We present the effect of A-site double doping (La0.254Y0.746) on elastic and thermal properties of EuVO3 in a wide doping range (0≤x≤1), using a modified rigid ion model (MRIM). Various lattice distortions and their relation to bulk modulus has been investigated systematically. The effect of the lattice distortions on thermodynamic properties of Eu1−x (La0.25Y0.74) x VO3 has been explored by an atomistic approach. The computed results emphasize that the Debye temperature decreases while the specific heat increases with increase in doping concentration (x). The computed temperature dependent (1 K≤T≤300 K) specific heat trends are in accordance with the corresponding experimental data at various compositions. Future scope of MRIM has also been discussed.

The thermal and mechanical properties of orthocobaltates, ACoO3 (A = Sm, Tb, Dy, Ho, and Er), have been investigated using the modified rigid ion model (MRIM) by incorporating the effect of lattice distortions. We have computed the variations of specific heat and thermal expansion coefficient for these orthocobaltates in wide temperature range of 1 K (−272 °C) ≤ T ≤ 1000 K (727 °C). The calculated results of specific heat, thermal expansion, bulk modulus, and other thermal and mechanical properties accord very well with the available experimental data, implying that MRIM represents properly the nature of the perovskite-type rare earth cobaltates. In addition, we have also reported the results on molecular force constant (f), Reststrahlen frequency (υ), cohesive energy (ϕ), Debye temperature (θD), and Gruneisen parameter (γ).

The thermodynamic study of vanadates is particularly interesting, as these compounds undergo multiple orbital and magnetic ordering transitions resulting in structural phase transitions as a function of temperature. The elastic and thermal properties have been computed by considering the intriguing temperature dependent structural phase transitions. A detailed investigation of lattice distortions, bulk modulus, cohesive energy and Debye temperature of the doped vanadium compounds Y1−xLaxVO3 (0 ≤ x ≤ 1) has been accomplished. The temperature dependence of specific heat (1 K ≤ T ≤ 300 K) and low temperature thermal expansion is probed over the whole doping range. The results obtained are compared with the earlier experimental data to validate the application of modified rigid ion model to describe elastic and thermal behavior of the La doped YVO3.

The thermodynamical and allied properties of (Pr 1− y Sm y ) 0.7 Ca 0.3 CoO 3 (0 ≤ y ≤ 1) were investigated in this paper by means of a modified rigid ion model (MRIM) with pair wise interatomic interaction potential. The calculated specific heat, bulk modulus, and other thermal properties reproduce well with the available experimental data, implying that MRIM represents properly the nature of the perovskite type cobaltates. The specific heats are found to increase with temperature and decrease with concentration ( y ) for the present cobaltates. The increase in Debye temperature ( θ D ) indicates an anomalous softening of the lattice specific heat due to increase in T 3 -term in the specific heat occurs with the decrease of y .

We have calculated the thermal and allied properties of La 1− x A x CoO 3 ( A =K, Cd, Pr, Nd and 0≤ x ≤1) as a function of temperature 1 K≤ T ≤300 K for the first time using Modified Rigid Ion Model (MRIM). The calculated bulk modulus, specific heat, thermal expansion and other thermodynamic properties obtained from MRIM have presented proper interpretation of the experimental data, for monovalent (K + ), divalent (Cd 2+ ) and trivalent (Pr 3+ and Nd 3+ ) ion-doped LaCoO 3 . In addition, the results on the cohesive energy ( ϕ ), molecular force constant ( f ), Reststrahlen frequency ( υ ), Debye temperature ( θ D ) and Gruneisen parameter ( γ ) are also discussed.

A single phase polycrystalline hexagonal YMn0.8Ru0.2O3 compound with space group P63cm (25-1079) have been synthesized by using solid state reaction method at sintering temperature 1280°C. The detailed low temperature electrical properties were evaluated over a broad range of temperature. The temperature dependence of the dc resistivity at low temperature reveals the semiconducting behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the ;temperature scale T* ~ 1.05 × 106 K and finally the density of state at Fermi level N(EF) is calculated to be ~ 5.6 × 1019 eV−1 cm−3.

We have computed the effect of strontium doping on the thermophysical properties of perovskite structure rare earth cobaltate, La 1− x Sr x CoO 3 (0.0≤ x ≤1.0) by means of a rigid ion model (RIM) in the temperature 0 K 2 ≤ T 2 ≤100 K 2 . The trends of variation of our computed specific heat with temperature are in agreement with corresponding experimental data. A meticulous attention was given to the investigation of the assumption that these cobaltate perovskites are Debye-like solids and obeys T 3 law at low temperature ( T θ D /50). Present investigations reaffirm the presence of strong electron–phonon interactions in these compounds. An interesting phenomenon was observed in C p / T vs. T 2 plot for x ≤0.2 below 15 K where linearity deviates, which suggests the gradual freezing of the entropy on cooling. In addition, the results on bulk modulus ( B ), cohesive energy ( ϕ ), molecular force constant ( f ), restsrahlen frequency ( υ ), and Debye temperature( θ D ) are also presented. The scope of further extension of the present model has also been discussed.

A systematic series of polycrystalline compounds of YBaCo4−xNixO7 (0 ≤ x ≤ 0.3) have been synthesized by conventional solid-state reaction technique in order to scrutinize comprehensively the effect of Ni substitution on structural, micro-structural and electrical transport properties. X-ray diffraction patterns recorded at room temperature illustrate the structural phase transition with Ni from hexagonal (P6 3 mc) phase symmetry to trigonal (P31c) phase symmetry. The grain morphology observed via scanning electron microscopy indicates the decrease in grain size with increasing Ni percentage. The EDS analysis indicates that Ni is distributed randomly on Co sites also supports the change in crystal structure. The calculated electrical resistivity revealed the semiconducting nature of all compound with and without magnetic field. The resistivity data supported by using Mott’s variable range hopping (VRH) model to calculate the hopping distance (Rh), hopping energy (Eh) and density of states at Fermi level N(EF). Moreover, resistivity data are well fitted with small polaron hopping (SPH) model to investigate the conduction behaviour in the system. Thus, conduction mechanism carried out electronically induced structural phase changes involves in Ni–O–Ni and Ni–O–Co bond angles and bond lengths.

In the present paper, the thermophysical properties of PrCoO 3 cobaltates is mapped here with reference to the changed local environment at A-site due to calcium doping for the first time using Rigid Ion Model (RIM). The specific heat and there by thermal expansion for temperature (1 K ≤ T ≤ 1000 K) of Pr 1− x Ca x CoO 3 ( x = 0.0–0.5) are presented. The trends of variation of our computed results on specific heat with temperature are in more or less similar with corresponding experimental data for almost all the compositions ( x ) of Pr 1− x Ca x CoO 3 . Strong electron–phonon interactions are present in these compounds which causes the variation of the lattice specific heat ( C v (lattice) ) with cation doping of varying size and valence. In addition, we have computed the thermal expansion ( α ), bulk modulus ( B ), cohesive energy ( ϕ ), molecular force constant (ƒ), and Restsrahalen frequency ( υ ) whose results are discussed in detail.

The thermal properties of La1−x A x CoO3 (A = Ca, Ba and 0.0≤x≤0.3) for temperature (1 K≤T≤300 K) have been investigated using the Modified Rigid ion model (MRIM) with pair wise interionic interaction potential. The temperature dependent (1 K≤T≤300 K) variation of specific heat and thermal expansion for La1−x A x CoO3 (A = Ca, Ba and 0.0≤x≤0.3) has presented proper interpretation of the experimental data. Also the effect of lattice distortions on the thermal properties of these perovskite cobaltates has been studied by an atomistic approach. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θ D ) and Gruneisen parameter (γ) are also discussed.

The bulk modulus and thermal properties of orthovanadates SmVO3 and EuVO3 in the temperature range 5 K≤T≤300 K have been investigated using the Modified Rigid Ion Model (MRIM) by incorporating the effect of lattice distortions. The results on the specific heat, cohesive energy, molecular force constant, the reststrahlen frequency and the Gruneisen parameter following the temperature driven structural phase transitions are presented. Our results are in fair agreement with the available experimental data. The specific heat results can further be improved by including the spin and orbital ordering contributions to the specific heat.

The thermal and allied properties of rare earth orthogallates LnGaO 3 (Ln = La, Ce, Nd, Pr), La 1− x Ce x GaO 3 , La 1− x Pr x GaO 3 and La 1− x Nd x GaO 3 ( x = 0.2, 0.4, 0.6, 0.8) were investigated in this work by means of a Modified Rigid Ion Model (MRIM). Theoretically, MRIM provides arguably the most realistic interaction potential to treat these properties. We have computed the variation of specific heat and volume thermal expansion coefficient for these orthogallates in wide temperature range (0 K ≤ T ≤ 1200 K). The computed results on Bulk modulus (B), Debye temperature ( θ D ) and specific heat ( C P ) obtained from MRIM have presented proper interpretation of the experimental data for LnGaO 3 (Ln = La, Ce, Nd, Pr) compounds. The specific heat results can be further improved by including the crystalline electric field contribution to the specific heat.

We have investigated the bulk modulus and thermal properties of orthovanadates RVO 3 (R = La, Ce, Pr, Nd) probably for the first time in both monoclinic and orthorhombic phase by incorporating the effect of lattice distortions using the Modified Rigid ion model (MRIM). The calculated bulk modulus, specific heat and other thermal properties reproduce well with the available experimental data, implying that MRIM represents properly the nature of the perovskite type vanadates. The specific heat results can further be improved by including the spin and orbital ordering contributions to the specific heat.

We have reported the temperature dependence (5 K ≤ T ≤ 1000 K) of the lattice contribution to the specific heat of rhombohedral LaCoO3 and orthocobaltates RCoO3 (R = Pr and Nd). The strong electron phonon interactions are present in these compounds and lattice distortions can affect them substantially. Thus Rigid Ion Model (RIM) is used for the first time to study the cohesive and thermal properties of the cobaltates RCoO3 with rare earth cation (R = La, Pr and Nd). The values of specific heat calculated by us have shown remarkably good agreement with corresponding experimental data. In addition, the results on the temperature dependence of cohesive energy (ϕ), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θD) and Gruneisen parameter (γ) are also reported.

We have investigated the elastic and thermodynamic properties for the perovskite type metavanadate SrVO3 and the multiferroic PbVO3, probably for the first time by the means of a Modified Rigid Ion Model (MRIM). We present the elastic constants (C11, C12, C44) and other elastic properties like Bulk modulus (B), Young′s modulus (E), shear modulus (G), Poisson′s ratio (σ) and wave velocity (υl, υs, υm). Besides we have reported the thermodynamic properties molecular force constant (f), Reststrahlen frequency (ν), cohesive energy (ϕ), Debye temperature (θD) and Gruneisen parameter (γ). We have also computed the variation of heat capacity (CP) and there by volume thermal expansion coefficient (α) in a wide temperature range. We found that the computed properties reproduce well with the available data in literature. To our knowledge some of the properties are reported for the first time.

A shell model has been used to study the structure, phonon dynamics and phase coexistence of perovskite manganites RMnO3 (R=Tb, Dy, Ho). The calculated crystal structure, Raman and IR frequencies and specific heats are found to be in good agreement with the available experimental data. The phonon density of states, elastic constants, elastic stiffness, shear constants and phonon dispersion curves have been computed for these manganites. A zone center imaginary Au mode is revealed in these phonon dispersion curves, which indicates the occurrence of the metastability of the perovskite phase. The Gibbs free energy values calculated as a function of temperature and pressure for RMnO3 in the orthorhombic phase, when compared with those of the hexagonal phase, reveal the possibility of coexistence of these two phases in the present multiferroic manganites under ambient conditions.

Magnetic and dielectric properties of the double perovskite compounds of the type R 2CuTiO6 (RCTO, where R=Y, La, Pr and Nd) has been studied. Y2CuTiO6 (YCTO) crystallizes in a hexagonal unit cell, whereas the other three compounds form into orthorhombic structure. All four compounds show paramagnetic behavior down to 5 K. The dielectric studies show moderate dielectric constant (e′) and very small dielectric loss (tan δ) for YCTO. The orthorhombic members of RCTO compounds exhibit moderate values of e′ and tan δ. The dielectric properties are presented and discussed here in the light of the influence of structure and rare-earth ions on the physical properties of RCTO compounds.

We have investigated the transport studies of the Nb-doped Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) manganites for the first time for identifying the transport properties as a function of the composition and temperature. Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) samples exhibit a single phase nature with an orthorhombic structure and a Pbnm space group. These materials show colossal magnetoresistance effect (CMR) and have wide technological applications such as magnetic sensors, reading head devices, spintronics, bolometers, magnetic refrigeration, etc. The computed transport properties such as cohesive energy, Reststrahlen frequency, Debye temperature, Gruneisen parameter and temperature dependence of specific heat of Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) manganites are discussed in detail in the present work by applying extended rigid ion model (ERIM) and have shown significant agreement with the corresponding available results.

We have investigated the thermal properties and specific heat of earth mantle silicates ASiO3 (A = Mg, Ca) by the means of rigid ion model (RIM) and compared them with the earlier experimental reports. The calculated specific heat of ASiO3 (A = Mg, Ca) obeys T3 law at low temperature (T < θD/50). The temperature dependence of the specific heat of MgSiO3 and CaSiO3 (0 K ≤ T ≤ 2000 K) is presented along with the elastic, cohesive and thermal properties, like Bulk modulus (B), cohesive energy (φ), molecular force constant (f), reststrahlen frequency (ν), Debye temperature (θD) and Gruneisen parameter (γ) at T = 300 K.

We report a colossal resistance drop around insulator–metal transition temperature ( T MI ) in Sm 0.55 Sr 0.45 MnO 3 induced by direct current. Polycrystalline samples of Sm 0.55 Sr 0.45 MnO 3 were synthesized through solid state reaction method. They have been investigated by X-ray diffraction for phase evaluation, scanning electron microscopy for grain morphology and dc resistivity measurement techniques for resistivity–temperature behavior. The resistivity–temperature behavior has been measured with different biasing currents (1 mA, 2.5 mA, 5 mA, 10 mA and 50 mA). With increasing biasing current, the resistivity of the samples decreased drastically. The change in the resistivity of the samples for bias currents 1 mA and 50 mA at T MI was found to be ∼2560%. This phenomenon of electroresistance is discussed in view of strong interaction between carrier spins and localized spins in Mn ions and percolative mechanism of phase-separation.

In the present work, the specific heat of La0.5(Ca0.5−xCdx)MnO3 double doped manganites at the doping concentrations x = 0.0–0.5 are computed for the first time for understanding the thermodynamic behaviors in manganites using interatomic potential by Renu Choithrani et al. The crystal structure of given manganites with space group Pnma have an orthorhombic structure except La0.5Cd0.5MnO3, which instead shows a rhombohedral (R3c) space group. These materials find extensive technological applications in magnetic sensors, computer hard drive reader, logic devices, etc. The interatomic potential has been applied to study the specific heat (Cp) as a function of temperature. The trends of variation of our computed specific heats with temperature are in agreement with corresponding experimental data by Wang et al. for almost all the compositions (x) of La0.5(Ca0.5−xCdx)MnO3 with minor deviations at higher temperatures. The specific heats are found to increase with temperature from 2 to 300 K. The values of specific heats also increase with composition (x) when we go from x = 0.0 to 0.5 in these manganites. These features are exhibited by both the experimental and our theoretical results. In addition, we have used modified rigid ion model (MRIM) developed from the interatomic potential to compute the thermodynamical parameters whose results are discussed in detail for the present system of Cd-doped manganites.

The effect of strontium (Sr) doping on the structural, magnetic, electrical, and thermal properties of Pr1-xSrxCoO3 (0.1 ≤ x ≤ 0.5) has been studied. The samples were synthesized by using the conventional solid-state reaction method. The Rietveld refinement of X-ray diffraction patterns confirms the single-phase composition with orthorhombic (Pbnm) perovskite symmetry. The magnetization measurements revealed the paramagnetic to ferromagnetic transition and the transition temperature (Tc) increased with increasing Sr doping. The effective magnetic moments determined by the Curie-Weiss law show an increase in the Sr concentration. The temperature dependence of electrical resistivity suppressed with increasing the Sr content. Moreover, all the compounds other than x = 0.5 show the semiconducting nature. All semiconductor compositions (x = 0.1, 0.2, 0.3, and 0.4) in the high temperature region can be explained within the framework of the small polaron hopping model and the variable range hopping model, wherea...

We have incorporated the translational rotational (TR) coupling effects in the framework of three body force shell model (TSM) to develop an extended TSM (ETSM). This ETSM has been applied to reveal the second order elastic constants ( C 11 , C 12 and C 44 ) in the dilute regimes 0≤ x ≤0.50. Our theoretical results have reproduced well the observed variations of C 11 ( x =0.14, 0.43) and C 12 ( x =0.14, 0.43) with temperature. The anomalous elastic behaviour observed in C 44 below 150 K for x =0.43 has been predicted well by ETSM results in the orientationally disordered (NH 4 I) x (KI) 1− x mixed crystals. Our results for C 12 are in good agreement with the experimental data available for x =0.14 and 0.43. Besides, the third and fourth order elastic constants and the results on cohesive and thermophysical properties are also discussed.