Thermostructural and Elastic Properties of PbTe and Pb0.884Cd0.116Te: A Combined Low-Temperature and High-Pressure X-ray Diffraction Study of Cd-Substitution Effects

Roman Minikayev,Andrzej Katrusiak,Fatemeh Safari,Wojciech Paszkowicz,Anthony Bell,Wojciech Szuszkiewicz,Andrzej Szczerbakow,Elżbieta Dynowska

doi:10.3390/cryst11091063

Abstract

Rocksalt-type (Pb,Cd)Te belongs to IV–VI semiconductors exhibiting thermoelectric properties. With the aim of understanding of the influence of Cd substitution in PbTe on thermostructural and elastic properties, we studied PbTe and Pb0.884Cd0.116Te (i) at low temperatures (15 to 300 K) and (ii) at high pressures within the stability range of NaCl-type PbTe (up to 4.5 GPa). For crystal structure studies, powder and single crystal X-ray diffraction methods were used. Modeling of the data included the second-order Grüneisen approximation of the unit-cell-volume variation, V(T), the Debye expression describing the mean square atomic displacements (MSDs), <u2>(T), and Birch–Murnaghan equation of state (BMEOS). The fitting of the temperature-dependent diffraction data provided model variations of lattice parameter, the thermal expansion coefficient, and MSDs with temperature. A comparison of the MSD runs simulated for the PbTe and mixed (Pb,Cd)Te crystal leads to the confirmation of recent findings that the cation displacements are little affected by Cd substitution at the Pb site; whereas the Te displacements are markedly higher for the mixed crystal. Moreover, information about static disorder caused by Cd substitution is obtained. The calculations provided two independent ways to determine the values of the overall Debye temperature, θD. The resulting values differ only marginally, by no more than 1 K for PbTe and 7 K for Pb0.884Cd0.116Te crystals. The θD values for the cationic and anionic sublattices were determined. The Grüneisen parameter is found to be nearly independent of temperature. The variations of unit-cell size with rising pressure (the NaCl structure of Pb0.884Cd0.116Te sample was conserved), modeled with the BMEOS, provided the dependencies of the bulk modulus, K, on pressure for both crystals. The K0 value is 45.6(2.5) GPa for PbTe, whereas that for Pb0.884Cd0.116Te is significantly reduced, 33.5(2.8) GPa, showing that the lattice with fractional Cd substitution is less stiff than that of pure PbTe. The obtained experimental values of θD and K0 for Pb0.884Cd0.116Te are in line with the trends described in recently reported theoretical study for (Pb,Cd)Te mixed crystals.

Highlights

IntroductionThe achievable alloying level for such materials depends on the substituent and preparation method
The PbTe and Pb1−xCdxTe single crystals were obtained by the self-selecting vapor growth (SSVG) method described in refs. [88,89]
For pure PbTe, most of these properties were known in advance, but the information regarding temperatures below 105 K has been mostly based on the results of neutron powder diffraction of ref

Summary

Introduction

The achievable alloying level for such materials depends on the substituent and preparation method. Such substitution significantly affects the thermoelectric properties and others. We recognized that a determination of thermostructural and elastic properties can contribute to development of these materials, and that detailed studies involving the structure analysis under nonambient pressures and temperatures are lacking for mixed (IV,II)VI semiconductors. This observation gave us motivation to undertake the study for Pb1−xCdxTe, which is one of most studied thermoelectric materials

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Conclusion