Pressure and temperature induced structural, electronic and thermal properties of CdAl2Se4

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Abstract

We present a comprehensive computational study on the ground state properties of CdAl2Se4; a defect chalcopyrite compound. Considering its potential application, we have calculated the electronic band structures using the full potential linear augmented plane wave method within the density functional theory at ambient conditions and higher pressure and temperatures. The obtained Density of states at ambient conditions compares favourably with the available experimental and theoretical results. Our calculated band gap is in excellent agreement with experimental results. Thermal effects are obtained employing quasi-harmonic Debye model. The changes in properties associated with the electronic structure of CdAl2Se4 are evaluated at various temperatures and pressures.

Highlights

► FP-LAPW study of structural, electronic and thermal properties of CdAl2Se4. ► Structural parameters are in good agreement with the experimental data. ► Calculated electronic band gap at ambient and higher pressure and temperature is found to be direct. ► Explored the effect of temperature and pressure on electron and hole pockets. ► Thermal effects are obtained employing quasi harmonic Debye model.

Introduction

The scientific researches in optoelectronic materials have attracted great attentions during recent years. Defect chalcopyrite compounds like AB2X4 (X=Se, Te, S) possess numerous high technological applications [1], [2], [3], [4]. These ternary defect compounds are of high interest because of the presence of stoichiometric vacancies, which facilitate the doping by impurities and the formation of a solid solution [5], [6]. Various type of impurities including magnetic impurities can be doped into the vacancies to design a new class of materials like dilute magnetic semiconductors (DMS) for spintronics applications [7]. Moreover, these compounds also exhibit a very low sensitivity to unwanted impurities and a high resistance to ionization radiation [8]. In this perspective the most studied defect chalcopyrite compound is CdAl2Se4; it is a potentially attractive material for various optoelectronic applications. Along with extensive experimental efforts, several theoretical efforts have been devoted to the study of structural electronic and optical properties of this compound at ambient conditions [9], [10], [11], [12], [13], [14]. UV-photo detectors based on this compound have already been used in devices [15]. The unit cell parameters for the BCT structure of CdAl2Se4 are available through the X-ray diffraction technique. The knowledge of the structural and electronic properties of a compound at extreme conditions are of fundamental scientific interest as they help us to understand, characterize, and predict mechanical properties of materials in surroundings and under extreme conditions. Pressure induced phase transitions in CdAl2Se4 have recently been studied experimentally by Meenakshi et al. [13] and theoretically by Fuentes-Cabrera and Sankey [11]. Calculations related to the analysis of structural and electronic properties of the present material under higher temperature and higher pressure have not been done so far. Thermodynamical properties of CdAl2Se4 are also untouched. Earlier we have reported our results for ZnAl2Se4 defect chalcopyrite compounds [16], [17], therefore, in this communication we will provide missing information related to the above mentioned properties. In order to show the behaviour of the material under thermal effect, the obtained first-principles results are used as input in the quasi-harmonic Debye model [18].

Section snippets

Method of calculation

The considered CdAl2Se4compound is assumed to take a defect chalcopyrite structure in space group I-4. The Wyckoff positions in the primitive cell are: for Cd 2a (0, 0, 0), for Al1 2b (0, 0, 0.5), for Al2 2c (0, 0.5, 0.25) and for Se 8 g (x,y,z),(x,y,z),(y,x,z),(y,x,z) where x,y and z are the internal parameters. To calculate the ground state properties, we have used a full potential linear augmented plane wave plus local orbitals method (FPLAPW +lo) as embodied in the WIEN 2 k package,

Structural properties

The obtained results in defect chalcopyrite compound CdAl2Se4 at P=0GPa and T=0K are compared with existing data in Table 1. Our structural parameters, i.e., the lattice constants and the anion internal parameters x,y and z are in good agreement with the earlier theoretically predicted constants. For instance our calculated structural parameters using the LDA functional are very close to the results by Ouahrani et al. [14] and Fuentes-Cabrera and Sankey [11]. Overall the calculated lattice

Conclusions

We present the results of local density approximation based investigation using the self-consistent full potential linear augmented plane wave method. We investigated the effect of three different exchange correlations functional on electronic band gap and our calculated band gap by EV-GGA formalism at P=0GPa and T=0K is 3.07 eV, which matches exactly with the experimental result. We also have explored the effect of temperature and pressure on change in the band structures and electronic

Acknowledgments

One of the authors (UPV) acknowledges the financial assistance provided by MPCST, Bhopal, sanction no. 1928/CST/R&D/08 and UGC, New Delhi F. No. 36-124/2008(SR).

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