Density functional theory studies on elastic and electronic properties of tetragonal ZnP 2 Zhenhua Yang a, b, c , Xianyou Wang a, b, c, * , Li Liu a, b, c , Shunyi Yang b, c , Xuping Su c a Faculty of Materials, Optoelectronics and Physics, Key Laboratory of Low Dimensional Materials & Application Technology of Ministry of Education, Xiangtan University, Xiangtan 411105, Hunan, China b School of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, Xiangtan 411105, Hunan, China c Key Laboratory of Materials Design and PreparationTechnology of Hunan Province, Xiangtan University, Xiangtan 411105, Hunan, China article info Article history: Received 19 January 2011 Received in revised form 6 June 2011 Accepted 10 June 2011 Available online 16 June 2011 Keywords: Tetragonal ZnP 2 First-principles Elastic properties Anisotropy abstract The lattice constants, elastic properties, Debye temperature and electronic structure of polycrystalline tetragonal ZnP 2 were calculated by first-principles density functional theory calculations. The six inde- pendent elastic constants C 11 , C 12 , C 13 , C 33 , C 44 , and C 66 of tetragonal ZnP 2 were analyzed. The bulk modulus (B), shear modulus (G), Young’s module (E), and elastic anisotropy of polycrystalline tetragonal ZnP 2 were evaluated. The results showed that the tetragonal ZnP 2 has large elastic isotropy in compressibility and small elastic anisotropy in shear. Besides, the electronic structure of tetragonal ZnP 2 was studied, which indicates a mixture of ionic bond and covalent bond between Zn and P atoms. Ó 2011 Elsevier Masson SAS. All rights reserved. 1. Introduction Li-ion battery is a very promising candidate for powering elec- tric vehicles due to their high energy density and good safety [1,2]. As carbon can form LiC 6 with Li metal and present a low discharge potential plateau, the carbon materials have been commercially used as the anode material of Li-ion battery. However, theoretical capacity of carbon anode materials is only 372 mAh/g [3]. In order to further improve the energy density of Li-ion battery, develop- ment of the novel anode materials with higher discharge capacity is a hot topic. Recently, ZneP compounds have aroused great interests because of their excellent theoretical capacity. Tetragonal Zn 3 P 2 , ZnP 2 , and monoclinic ZnP 2 have been intensively investigated and used as anode materials for Li-ion batteries [4e6]. Among various ZneP compounds, tetragonal ZnP 2 displays interesting structure, high first discharge capacity (1340 mAh/g) and large charge capacity (1107 mAh/g). Besides, although tetragonal ZnP 2 shows relatively good cyclability (350 mAh/g after 100 cycles) [4], its capacity loss was still obvious. When tetragonal ZnP 2 reacts with lithium, the electrochemical lithiation/delithiation process occurs. Significant volume change appears as a result of Li-doping, which may break the lattice structure of electrode material and lead to capacity loss. The study of elastic properties of tetragonal ZnP 2 is useful to understand the stability of anode materials with Li-doping. C.L. Fan et al. studied the structure and electronic properties of tetragonal ZnP 2 at high pressure based on the first-principles density theory calculations, it is found that the structural and electronic properties of tetragonal ZnP 2 at high pressure are quite stable [7]. To the best of our knowledge, no other theoretical studies on tetragonal ZnP 2 were reported. The elastic properties of tetragonal ZnP 2 are important because they are closely related with applications of tetragonal ZnP 2 . For example, the bulk modulus is related to the hardness of material. Shear modulus is a measurement of resistance to reversible deformations upon shear stress. Young’s modulus is used to estimate the stiffness of materials and Poisson’s ratio which is defined as the ratio between diatropic strain and longitudinal strain. The investigation on elastic properties of tetragonal ZnP 2 will help us to understand mechanism of electrode particle fracture. To further understand physical properties of tetragonal ZnP 2 , the elastic properties, Debye temperature and electronic structure of tetragonal ZnP 2 are investigated via first-principles density functional calculations in this paper. * Corresponding author. Tel.: þ86 731 58292060; fax: þ86 731 58292061. E-mail address: wxianyou@yahoo.com (X. Wang). Contents lists available at ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2011.06.008 Solid State Sciences 13 (2011) 1604e1607