First principles study of the electronic structure and birefringence properties of Ba3(PS4)2,YPS4,Pb3(PS4)2,and BiPS4
The theoretical electronic structure and optical properties were analyzed using density-functional theory for metal thiophosphates composed of P-S coordination tetrahedra with four different cations,including Ba3(PS4)2,YPS4,Pb3(PS4)2,and BiPS4.As the atomic radius of the metal cations increases,the(PS4)3-groups bind to these cations,resulting in higher dielectric constants of the compounds.The calculated energy gaps reveal that Ba3(PS4)2 and Pb3(PS4)2 have indirect band gaps of 2.074 eV and 2.271 eV,respectively,while YPS4 and BiPS4 exhibit direct band gaps of 2.105 eV and 1.534 eV,respectively.All compounds show p-p hybridization of P-and S-atom orbitals.The static dielectric constants for Ba3(PS4)2,YPS4,Pb3(PS4)2,and BiPS4 are determined to be 5.41,5.44,7.26,and 8.22,respectively.The birefringence magnitudes at 1064 nm for Ba3(PS4)2,YPS4,and BiPS4 are 0.068,0.162,and 0.125,respectively,while Pb3(PS4)2 belongs to the cubic crystal system and has a birefringence of zero.Charge density diagrams and layout analyses indicate that the P-S bonds are covalent,while the Y-S,Pb-S,and Bi-S bonds are all strongly ionic.The anisotropy magnitude follows the order of YPS4＞BiPS4＞Ba3(PS4)2,whereas Pb3(PS4)2 is isotropy.
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