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We have evolved an effective interionic interaction potential to investigate the pressure-induced phase transitions from zinc blende (B3) to rock salt (B1) structure in II-VI [ZnSe] semiconductors. The elastic constants, including the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach, are deduced. Keeping in mind that both of the ions are polarisable, we employed the Slater-Kirkwood variational method to estimate the vdW coefficients. The estimated value of the phase transition pressure (P t ) is higher than in the reported data, and the magnitude of the discontinuity in volume at the transition pressure is consistent with that data. The major volume discontinuity in the pressure-volume phase diagram identifies the structural phase transition from zinc blende to rock salt structure. The variation of second-order elastic constants with pressure resembles that observed in some binary sem...

A theoretical study of the high-pressure phase transition and elastic behavior in diluted magnetic semiconductors Zn 0.83 Mn 0.17 Se, using a three-body interaction (TBI) potential caused by the electron-shell deformation of the overlapping ions is carried out. The estimated values of phase transition pressure and the vast volume discontinuity in pressure-volume (PV) phase diagram indicate the structural phase transition from zincblende (B3) to rock salt (B1). The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. The inconsistency in the deduced value of pressure derivative of second order elastic constant with the available data is attributed to the fact that we derive expressions neglecting thermal effects and assuming the overlap repulsion significant only up to nearest neighbors. The vdW interaction is effective in obtaining the thermodynamical parameters such as Debye temperature, Gruneisen parameter, thermal expansion coefficient, compressibility as well phase stability in diluted magnetic semiconductors. It is revealed that TBI model has a promise to predict the phase transition pressure and the pressure variation of elastic constants of other semiconductors as well.

An effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in lanthanum monochalcogenides LaX [X = S, Se, Te] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (P t ) and the magnitude of the discontinuity in volume at the transition pressure are consistent with the reported data. A large volume discontinuity in the pressure-volume phase diagram identifies the structural phase transition from B1 to B2 structure. We also study the second order elastic constants for these La compounds. It appears that the vdW interaction is effective in determining the elastic and structural properties of these test compounds.

The reported specific heat C (T) data of the perovskite manganites La1-x Ca x MnO3, with x = 0.1, 0.2 and 0.33, is theoretically investigated in the temperature domain $4 \le T \le 10$ K. Calculations of C (T) have been made within the two component scheme: one is the Fermionic and the other is Bosonic (phonon or magnon) contribution. Lattice specific heat is well estimated from the Debye model and Debye temperature for Ca doped lanthanum manganites is obtained following an overlap repulsive potential. Fermionic component as the electronic specific heat coefficient is deduced using the band structure calculations for ferromagnetic metallic phase. Later on, for x = 0.1, following double exchange mechanism the role of magnons is assessed towards specific heat and find that at much low temperatures (T < 10 K), specific heat increases and show almost T 3/2 dependence on the temperature. We note that, the lattice specific heat is smaller for x = 0.1 when compared to that of magnon specific heat below 10 K. For x = 0.2, i.e., in the ferromagnetic metallic phase the magnon contribution is larger with the electron contribution while the reverse is true for x = 0.33. It is further noticed that in the ferromagnetic metallic phase, electronic specific heat is small in comparison to the lattice specific heat in low temperature domain. The present investigations allow us to believe that electron correlations are essential to enhanced density of state over simple Fermi liquid approximation in the metallic phase of La1-x Ca x MnO3 (x = 0.2, 0.33). The present numerical analysis of specific heat shows similar results as those revealed from experiments.

The temperature-dependent specific heat C[Formula: see text](T) of nanocrystalline (NC) Cu (8 nm) and Pd (6 nm) is theoretically analyzed and compared with the specific heat of their corresponding bulk materials in the temperature range from 150 K to 300 K. It is revealed that the C[Formula: see text] values of NC Cu (Pd) are about 10% (40%) higher as compared to that of their corresponding bulk form, the softening of phonon frequencies at interfaces in NC materials is argumented as the main mechanism responsible for enhancement in C[Formula: see text] in the present work. Lattice (phonon) specific heat is obtained following an overlap repulsive potential using Debye model. In NC materials having large interface volume ratio, the phonon frequencies and Debye temperature are comparatively less at the interfaces than at the core of nanocrystal. The contributions to specific heat due to atoms present at interfaces (C[Formula: see text]) and those present at the core of nanocrystal (C[Formula: see text]) are estimated separately by estimating the characteristic Debye temperature ([Formula: see text]) from elastic force constant ([Formula: see text]). The temperature derivative of the internal energy yields the electronic contribution to specific heat (C[Formula: see text]). The present investigation based on the softening of phonon frequencies mechanism is successful to explain the enhancement in specific heat by nanocrystallization.

Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

The preparation of stable, uniform silver nanoparticles by reduction of silver acetate by ethylene glycol (EG) is reported in the present paper. It is a simple process of recent interest for obtaining silver nanoparticles. The samples were characterized by X-Ray diffraction (XRD), which reveals an average particle size (D) of 38 nm. The UV/Vis spectra show that an absorption peak, occurring due to surface plasmon resonance (SPR), exists at 319 nm.

Thermal conductivity κ(T) of LaFeAsO is theoretically investigated below the spin density wave (SDW) anomaly. The lattice contribution to the thermal conductivity (κph) is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and relaxation time below 150 K. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity dominates in LaFeAsO and is an artifact of strong phonon-impurity and -phonon scattering mechanism. Our result indicates that the maximum contribution comes from phonon scatters and various thermal scattering mechanisms provide a reasonable explanation for maximum appeared in κ (T).

The effect of bivalent cation Sr-doping on magnetic properties in multiferroic YMnO3 manganites was systemically studied by DC magnetic measurements. Both of the reported samples were prepared by solid-state reaction method with composition Y1−xSrxMnO3 (x = 0.00 and 0.03). The X-ray diffraction (XRD) results show that the compounds are synthesized in hexagonal crystal structure with space group P63cm (JCPDS: 25-1079) and slight increase in the lattice parameter is observed with strontium doping. The magnetisation versus temperature curve shows no clear anomaly near the antiferromagnetic transition temperature (TN), however from the magnetic measurements at 1000Oe a slight increase in the magnetisation is clearly witnessed with increasing Stront ium content to the Y-site.

The structural and elastic properties of thorium chalcogenides at high pressure, have been investigated using a suitable inter-ionic potential. The calculated equation of state, phase transition pressures for B1–B2 transition and bulk moduli for ThX (X=S,Se,Te) compounds agree well with the experimental results. ThTe, which crystallizes in the CsCl structure, does not show any structural transition up to 48 GPa. The present analysis does not show any anomalous features in elastic properties arising from ‘f’ electrons.

Nearly exponentially decaying heat capacity was observed exceptionally in a well-characterized naturally assembled hexagonal closed packed lattice of 4.0 nm nickel nanoparticles (NPs). It was also associated with quantum jumps. These were however not observed in other NP sizes and have negligible effects of high magnetic fields. Magnetic susceptibilities in contrast revealed the evolution of quantum size effects with a decrease in particle size. They exhibited sharp rise below about 30 K and vestiges of saturations below 5 K. The sharp rise was explained by Curie-like characteristics of odd electrons, while the saturations tend towards the orthogonal even-like case.

Iron-based superconducting layered compounds have the second highest transition temperature after cuprate superconductors. Their discovery is a milestone in the history of high-temperature superconductivity and will have profound implications for high-temperature superconducting mechanism as well as industrial applications. We have measured X-ray diffraction and Raman spectra of poly-crystalline FeTe1-xSex samples with x = 0.0, 0.5 and 1 at room temperature. X-ray profile of FeTe and FeTe0.5Se0.5 confirmed the primitive tetragonal unit cell. FeSe is found to be in double phase with tetragonal phase (about 66.62%) and orthorhombic (33.38%). A(1g) and B-1g phonon modes were observed in Raman spectra. At room temperature, these lines are located at 95 and 130 cm(-1) for FeTe, 93 and 129 cm(-1) for FeTe (0.5) Se (0.5) and 93 and 129 cm(-1) for FeSe samples.

Non-stoichiometric nickel oxide was synthesized by the thermal decomposition method at different sintering temperatures upto 1100 °C. The samples were analyzed by thermogravimetric analysis (TGA). Wherein, the stoichiometry of the sample was analyzed by calculating the excess oxygen. It was found that as the sintering temperature of the precursor increases the excess oxygen present in the sample decreases, and at temperature above 700 °C, the sample becomes stoichiometric. These results were interpreted as the decomposition temperature increases, which heals the defects present in the non-stoichiometric nickel oxide. Thus, highly defective nickel oxide at lower decomposition temperature approaches stoichiometric nickel oxide as the temperature is increases above 700 °C.

Compacted pellets of nanocrystalline nickel (NC-Ni) of average particle size ranging from 18 to 33 nm were prepared using a variety of surfactants. They were characterized well and were studied on the influence of the surfactants on the electrical resistivity and thermopower in the temperature range 5 to 300 K. It was found that the type of the surfactant used dominates over the average particle size in their electrical transport and the detail transport behaviors have been discussed. Moreover, the observed thermopower and resistivity features were contrasting compared to what are normally seen in the well-known materials. They are interpreted as indicative of attractive features these surfactants for the design of nanostructured thermoelectric materials with enhanced thermoelectric figure of merits., Comment: 21 pages, 8 figures, submitted to a journal, revised the manuscript in acknowledgement

We demonstrate here a very noteworthy nature of the critical roles of type of cappants, in addition to the particle size, on the electrical resistivity of compacted pellets of nickel nanoparticles (Ni-NPs) in the temperature range from 5 to 300 K that deviate significantly from highly conducting nature of a good metal yet without much deviation of the slopes. For this, face-centered cubic structured Ni-NPs of average particle size ranging from 18 to 33 nm were prepared using different polyol methods in the presence of various additional capping agents.

We have prepared CaMoO4:Tb@Fe3O4 hybrid nanoparticles by co-precipitation and polyol method. Their temperature kinetics for hyperthermia temperature ∼43 °C under different applied AC fields and the luminescence properties under UV-radiation are investigated. A strong green emission is observed due to the presence of Tb3+ ions.

Powders of Y1−xSrxMnO3 (x = 0.1 and 0.2) pervoskites were obtained by using conventional solid state reaction method and their electrical properties are carefully analyzed. The XRD pattern showed the pointed peaks which correspond to the hexagonal structure of the reported compounds with space group P63cm (25-1079). The resistivity versus temperature plot infers a semiconducting like behavior in both reported compounds. The suppression in the resistivity has been witnessed with increasing concentration Sr2+ ions at yttrium site. The small polaron hopping conductivity model adequately describes the electrical conductivity behavior. The activation energy (Ea) is found to decrease as the 'x' (Sr content) increases.

We report structural and transport properties of the polycrystalline orthorhombic GdMnO3 compound synthesized by using conventional solid state reaction method. The XRD pattern reveals the single phase formation of the reported compound in orthorhombic crystal structure with space group Pbnm (JCPDS: 25-0337). The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region. The effect of low temperature magnetic ordering can be clearly understood from the resistivity versus temperature plot. The calculated activation energy by using Arrhenius equation fitting are found slightly lesser than the reported value which indicates the lesser dense nature of the prepared compound.

We report the results of electrical resistivity, magnetic susceptibility and thermoelectric power measurements on the stoichiometric hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites. The resistivity and thermopower data show a metal-insulator phase transition for both samples. Magnetic susceptibility measurement confirms that both the samples undergo a transition from paramagnetic to ferromagnetic phase at defined Curie temperatures T(c) = 240 K (La(0.8)Ca(0.2)MnO(3)) and 263 K (La(0.8)Ce(0.2)MnO(3)). The electrical resistivity data are then theoretically analysed within the framework of the classical electron-phonon model of resistivity, i.e. the Bloch-Gruneisen model. Detailed analysis of the electrical resistivity of electron- and hole-doped manganites suggests that besides the electron-phonon effect another possibility for the change in carrier density arises due to the presence of electron correlation in the metallic system. From the thermopower S(T) results, we suggest that its behaviour is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between carrier diffusion and phonon drag contributions in the polycrystalline samples of hole-doped La(0.8)Ca(0.2)MnO(3) and electron-doped La(0.8)Ce(0.2)MnO(3) manganites.

We have performed Seebeck coefficient $(S)$ measurement for a series of high-quality ${\text{Na}}_{x}{\text{CoO}}_{2}$ single crystals for $0.23\ensuremath{\le}x\ensuremath{\le}0.84$ from 10 to 300 K. The room-temperature $S$ values were found to be around $30--100\text{ }\ensuremath{\mu}\text{V}/\text{K}$ and increase with increasing Na content. The temperature dependence of Seebeck coefficient of this system was found to be very sensitive for $x=1/2$, which is most likely due to the significant modifications of band structure as a result of the magnetic and charge orderings below 88 and 51 K. The overall observed features of the $S(T)$ were analyzed in the framework of a narrow-band model. The physical parameters obtained from the fitting provide a satisfactory description of the composition and temperature dependences of Seebeck coefficient in the ${\text{Na}}_{x}{\text{CoO}}_{2}$ system.

An effective interionic interaction potential (EIOP) approach is employed for the description of the pressure induced phase transitions of UxLa1−xS (x = 0, 0.4, 0.5 and 0.6) solid solutions. The long range Coulomb interaction with modified ionic charge, the van der Waals (vdW) interaction, and a short‐range repulsive interaction (up to second neighbor ions) are properly incorporated into the EIOP. We have obtained a reasonably good agreement between the theoretical and available experimental values for the phase transition pressures and elastic properties of UxLa1−xS compounds.

The temperature‐dependent resistivity of the perovskite manganites La0.78Pb0.22MnO3−δ is theoretically analyzed within the framework of the Bloch‐Gruneisen (BG) model. Due to inherent acoustic low‐frequency phonons as well as high‐frequency optical phonons, the contributions to the electron‐phonon resistivity have first been estimated. At low temperatures the acoustic phonons of the oxygen‐breathing mode yield a relatively larger contribution as compared to that of optical phonons. Furthermore, the nature of phonons changes around T = 215 K and a crossover from a acoustic phonons regime to a optical phonons with elevated temperature. The contribution to resistivity estimated by considering both phonons, when subtracted from experimental data, infers a T4.5 temperature dependence over most of the temperature range and understood in terms of electron‐magnon scattering within the double exchange process.

Pressure-induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in MgX [X = S, Se, Te] semiconductors are presented. An effective interionic interaction potential (EIOP) with long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach is developed. Particular attention is devoted to evaluate the vdW coefficients following the variational method, as both the cation and the anion are polarizable. Our result on vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from B1 to B2 structure. The estimated value of the phase transition pressure (Pt) is consistent with results previously published. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of NaCl type structure family.

In the present study Ag nanoparticles (NPs) of average particle size of 31-51 nm were prepared by the thermal decomposition method in the presence of appropriate concentration of Trioctylphosphine (TOP) and Oleylamine (OA). The X-ray diffraction measurements indicate the occurrence of face-centered cubic metallic Ag-NPs. The compacted pellets of these nanoparticles were investigated using thermoelectric power in the temperature range from 5 to 300 K. The observed thermoelectric power for all the samples are typical of a good metal and are found to be strongly dependent on grain size and the type of cappant used. The magnitude of thermo electric power increases as the particle size decreases. These results clearly indicate dominant role of disorder at grain boundaries and quantum confinement, which influence scattering of phonons and electrons in a significant way.

The thermoelectric properties of LaCo 1-x Cu x O 3-δ ceramics are theoretically analyzed, it is observed that thermoelectric figure of merit ZT ( = S2σT/κ) is maximized by Cu substitution in LaCo 1-x Cu x O 3-δ at x = 0.15. The lattice thermal conductivity (κ ph ) and phonon drag thermoelectric power [Formula: see text] were estimated by the scattering of phonons with defects, grain boundaries, electrons and phonon umklapp scattering to evaluate the thermoelectric figure of merit ZT. The Mott expression is used to estimate the electron diffusive thermoelectric power [Formula: see text] using Fermi energy as electron free parameter, [Formula: see text] shows linear temperature dependence. The electron contribution to thermal conductivity (κe) is estimated using temperature-dependent electron relaxation time. We found that Cu substitution increases the phonon scattering with grain boundaries and defects which significantly decrease the thermal conductivity and subsequently increase the thermoelectric power. The present numerical analysis of thermoelectric properties will help in designing more efficient thermoelectric materials for thermoelectric applications.

Pressure-induced structural aspects of ZnS-type (B3) to NaCl-type (B1) structure in XC (X = Si, Ge, Sn and Pt) compounds are presented. An effective interionic interaction potential with long-range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge is developed. Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. Our results on vast volume discontinuity in pressure volume phase diagram identify the structural phase transition from B3 to B1 structure. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data. The variations of elastic constants with pressure follow a systematic trend identical to that observed in other compounds of ZnS and NaCl-type structure family and the Born relative stability criteria are valid in XC compounds.

We report structure, electrical resistivity and thermopower of polycrystalline SmFe1-x CoxAsO samples for 0.0 ≤ x ≤ 0.3. The XRD data revealed full Co substitution at Fe-site with slight compression of the unit cell. Resistivity data showed that the spin-density wave observed at 130 K for x = 0 is suppressed when x = 0.05, above which superconductivity emerges due to injection of mobile electrons, supporting the substitution of Co3+ at Fe2+ site but disappears for x = 0.3. The thermopower (S) data indicate that the majority of charge carriers is electron-like and its value reaches −81 μV/K (at 300 K) for x = 0.3. Noticeable deviations from the expected linear behavior in S(T) at low temperatures and S/T against temperature curves at intermediate temperatures were observed. These observations were interpreted on the basis of nested Fermi surface and Umklapp processes.

We report the effect of strontium (Sr) doping on dielectric, magnetization, and thermodynamic properties of polycrystalline Y1−xSrxMnO3 (x = 0.1, 0.2) samples prepared by conventional solid-state reaction method. The temperature dependent dielectric permittivity and specific heat curves noticeably show the anomalies near its magnetic transition point, i.e., Neel temperature (TN), which are probably generated by the frustrated Mn3+ spins (S = 2) on a triangular Mn lattice showing the magneto-electric coupling between the electric and magnetic orders. However, the magnetic transition is not clearly evident in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Y3+ spins. The electronic transport mechanism in these materials was analyzed within the framework of conventional Arrhenius Law, i.e., ρ(T) = C exp(Ea/kBT) applied to low frequency ac resistivity data, and through the peak method employed to the permittivity and loss ta...

An effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions from ZnS-type (B3) to NaCl-type (B1) in XC [X = Si, Ge, and Sn] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data. The vast volume discontinuity in pressure volume phase diagram identifies the structural phase transition from B3 to B1 structure.

Nanocrystalline copper (NC-Cu) of average particle size (D) ranging from 29 to 55 nm was prepared using the polyol method. The compacted pellets of these nanoparticles were investigated using electrical resistivity (ρn) and thermopower (Sn) measurements in the temperature range from 5 to 300 K. The observed electrical resistivity and thermopower data for all the samples are typical of a good metal and the ρn(T) data are analyzed in the framework of the Bloch-Gruneisen theory. Our analysis indicates systematic departure from the bulk property for NC-Cu samples, decreasing effective Debye temperature, exponential decay of both the residual resistivity ratio (RRR) and the temperature coefficient of resistivity [α = (1/ρ)dρ/dT] as D decreases, yet the Boltzmann theory of electron transport still holds true (kFl ≫ 1). Further, the validity of the Nordheim-Gorter rule is also discussed. The temperature dependence of Sn is found to be quite sensitive as compared to bulk thermopower SBulk behavior, revealing the ...

We report the results of the Y substitution in Sr1−xYxSi2 with x≤0.15 via measuring the temperature-dependent electrical resistivity, thermal conductivity, as well as Seebeck coefficient. Upon substituting Y onto the Sr sites, the electrical resistivity exhibit semiconducting behavior and the room-temperature electrical resistivity tends to reduce for x≤0.08. The thermal conductivity also decreases with increasing the Y content. Moreover, the Seebeck coefficient has a substantial increase and a maximum of about 220 μV/K at around 80 K has been found for x=0.08. These promising effects lead to a significant enhancement in the thermoelectric performance characterized by the figure-of-merit, ZT. A room-temperature ZT value of approximately 0.4 is thus achieved for Sr0.92Y0.08Si2, about one order of magnitude larger than that of stoichiometric SrSi2.

Magnetotransport and thermal studies of Pr2/3Sr1/3MnO3 polycrystalline sintered bulk sample are reported here. The resistivity ρ(T) and thermoelectric power S(T) data show an insulator to metal (I-M) phase transition at TP≈294 K and TS≈290 K, respectively. Magnetization measurement confirms that the sample undergoes a transition from paramagnetic to ferromagnetic phase at a defined Curie temperature TC=280 K. A substantial increase in magnetoresistance from 2.5% at 280 K to 5% at 77 K has been noticed in a low magnetic field 0.15 T. Small polaron hopping model is found to be operative above the transition temperature TP, whereas electron-electron and electron-magnon scattering processes govern the low temperature metallic behavior. A detailed analysis of thermoelectric power in the ferromagnetic regime suggests that the complicated temperature dependence of S may be understood on the basis of electron-magnon scattering. A transition from decreasing high temperature thermal conductivity (due to local anhar...

We have employed an effective interionic interaction potential approach to describe the high-pressure phase transformation and mechanical properties of diluted magnetic semiconductors Zn1−xMxSe (M = Mn,Fe and Cd). This potential consists of the long-range Coulomb and three-body interactions (TBI) and the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbour ions and the van der Waals (vdW) interaction. Our calculated results have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 10,12,10 GPa) and the elastic properties of Zn1−xMxSe. The equation of state curves (plotted between V (P)/V (0) and pressure) for both the zincblende (B3) and rocksalt (B1) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses (ΔV (P)/V (0)) are also closer to the observed data. Further, the variations of the second- and third-order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other compounds of this family.

A comprehensive phenomenological calculation is reported for the pressure-dependent structural phase transition, equation of state and elastic properties of UxLa1−xS solid solution. We develop an effective interionic interaction potential incorporating the long-range Coulomb and the Hafemeister and Flygare form of short-range overlap repulsion extended up to the second-neighbour ions and van der Waals (vdW) multipole interactions. The overlapping of the f orbitals with the p orbitals of the nearest neighbour in UxLa1−xS that influences the effective Coulomb interactions is noticed to be a potential parameter in revealing the structural phase transition (from NaCl type (B1) to CsCl type (B2)) as well the equations of state of UxLa1−xS (x = 0,0.08,0.40,0.50,0.60,0.80 and 1.0) rare-earth compounds. The calculated results have revealed reasonably good agreement with the available data on the phase transition pressures (Pt = 25.5 (LaS), 30 (U0.08La0.92S), 34 (U0.40La0.60S), 35 (U0.50La0.50S), 47 (U0.60La0.40S), 59 (U0.80La0.20S) and 81 (US) GPa). The equation of state curves (plotted between V (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us are in fairly good agreement with the experimental results. Deduced values of the volume collapses [ΔV (P)/V (0) ] are also closer to their observed data. Further, the variations of the second- and third-order elastic constants with pressure have followed a systematic trend, that is almost identical to those exhibited by the measured and observed data in other compounds of NaCl-type structure family.

Pressure induced structural phase transformation and mechanical properties of NaCl-type (B1) to CsCl-type (B2) structure in uranium monochalcogenides (UX; X = S, Se, and Te) are presented. An effective interionic interaction potential is constructed, consisting of the long-range Coulomb and the Hafemeister and Flygare type short-range overlap repulsion extended up to the second-neighbour ions and the van der Waals (vdW) interaction. Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. Our calculated results have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 81, 21, 13 GPa) and the elastic properties of UX (X = S, Se, and Te). The equation of state curves (plotted between V (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses (ΔV (P)/V (0)) are also closer to their observed data. The variations of the second- and third-order elastic constants with pressure have followed systematic trends, which are almost identical to those exhibited by the measured and observed data in other compounds of the NaCl-type structure family.

We report the results of the electrical resistivity and Seebeck coefficient as well as thermal conductivity measurements on the stoichiometric CaAl(2)Si(2) and non-stoichiometric CaAl(1.75)Si(2.25), CaAl(1.9)Si(2.1), CaAl(2.1)Si(1.9), and CaAl(2.25)Si(1.75) compounds in the temperature range 10-300 K. It has been found that the magnitude of electrical resistivity decreases for the non-stoichiometric samples, attributed to the shift of Fermi energy from the dip of the density of states as a consequence of the changed Si/Al content. In addition, a systematic change in the magnitude of Seebeck coefficient as a function of Al/Si concentration has been observed. The results have been associated with the effect of hole/electron doping on the Fermi level density of states. A detailed analysis of the electrical resistivity and Seebeck coefficient suggests the presence of two types of charge carrier and the temperature dependent changes in their mobility. From the thermal conductivity results, we correlated the extent of disorder and Al/Si ratio with various thermal scattering mechanisms in the investigated temperature range.