Optoelectronic and thermoelectric response of Ca5Al2Sb6 to shift of band gap from direct to indirect
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The structural, optoelectronic and thermoelectric properties of Ca5Al2Sb6 under applied external pressures have been studied using the full potential linear augmented plane wave method. WIEN2k code is used with considering the generalized gradient approximation (GGA), modified Becke–Johnson (MBJ) and modified Becke–Johnson + spin orbit (mBJ + SO) functionals based on density functional theory (DFT). From electronic results, the size of the band gap decreases with increasing pressure and the nature of the band gap shift from direct to the indirect. In high pressure (>35.7 GPa by mBJ + SO), the band gap is also completely disappeared and the nature of compound is changed to the metallic. The calculated anisotropic optical properties such as the static dielectric function, increase with decreasing the size of band gap and increasing of pressure. As a novel result, the thermoelectric performance of n-type and p-type doping of Ca5Al2Sb6 is related to the value of pressure. According to the thermoelectric results, the n-type one has the highest ZT in comparison with the p-type Ca5Al2Sb6 material.
The authors are grateful to P. Blaha (Vienna University of Technology, Austria) for his technical assistance in using the WIEN2k code.
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