First principles study on the structural, elastic, electronic, optical and thermal properties of lead-free perovskites CsCaX3(X=F, Cl, Br)

Abstract

The physical properties included structural, mechanical, thermal and optical features of lead-free perovskites CsCaX3 (X = F, Cl, Br) have been investigated using abـinitio computations. The optimized lattice constants correspond extremely well with experimental as well as theoretical data. Structural stability of these phases is ensured from the Goldschmidt tolerance factor (tG) and formation enthalpy. Mechanical stability of CsCaX3 (X = F, Cl, Br) is authenticated by the investigated stiffness constants. The polycrystalline parameters such as bulk modulus (B), Poisson's ratio (ν), shear modulus (G), Young's modulus (E), anisotropy factor (A), hardness and Pugh's ratio are calculated and compared with similar types of compounds. The huge Young's modulus, bulk modulus as well as hardness of CsCaF3 assured that it has a great capacity to resists the deformation of volume as well as plastic than CsCaCl3 and CsCaBr3. The CsCaBr3 material is particularly ductile which makes it excellent for usage in thin films. The density of states (DOS) and the electronic band structures have been estimated of these compounds, which demonstrate that they have direct energy band gap that reduces continually in the order of CsCaF3>CsCaCl3>CsCaBr3. The optical features of CsCaX3 (X = F, Cl, Br) are investigated. Among the studied materials, the optical features of CsCaBr3 appear to be more enhanced than the other two compounds. A combined analysis of CsCaF3, CsCaCl3 and CsCaBr3 demonstrated that these types of materials have great potential for a variety of device applications in optical, ferroelectric, antiferromagnetic systems having their wide band gaps. Very low minimum conductivity of the studied phases confirmed the use of these compounds as thermal barrier coating compounds for industrial purposes.