摘要
基于密度泛函理论对P-S配位四面体与四种不同阳离子构成的金属硫代磷酸盐Ba3(PS4)2、YPS4、Pb3(PS4)2和BiPS4的电子结构和光学性质的理论机制进行分析.Ba3(PS4)2和Pb3(PS4)2为间接带隙,带隙分别为2.074和2.271 eV,YPS4和 BiPS4为直接带隙,带隙分别为2.105和1.534 eV.四种化合物在价带顶都产生P原子与S原子轨道的p-p杂化.并且得到Ba3(PS4)2、YPS4、Pb3(PS4)2和BiPS4的静介电常数分别为5.41,5.44,7.26和 8.22.Ba3(PS4)2、YPS4和 BiPS4 在 1064 nm 处的双折射率分别为 0.068,0.162 和 0.125,而 Pb3(PS4)2 属于立方晶系,双折射率为0;P-S键呈共价性,Y-S键、Pb-S键和Bi-S键皆具有较强的离子性.各向异性大小YPS4＞BiPS4＞Ba3(PS4)2,Pb3(PS4)2表现为各向同性.
Abstract
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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