负膨胀材料Zn_CN_2和Cd_CN_2晶格振动分析.pdfVIP

20 2 Vol1 20 No1 2 2008 6 THE JOU RNAL OF LIGHT SCAT TERING Jun1 2008 : 1004-5929(2008) 02-0145-06 Zn( CN) Cd( CN) 2 2 杜志勇, 梁二军 , 丁 佩, 王俊平, 徐二明 ( , , 450052) : Zn( CN) Cd( CN) , 2 2 Gr™neisen , , Gr™neisen 11 , Zn/ Cd , 223 cm- 1/ 154 cm- 1; 5 C S N ; 3 C S N ; 2 C S N 7 , 4 , C S N 3 Gr™neisen , , 47 cm- 1 Gr™neisen , : ; ; ; ; : O482. 2+ 3 : A Lattice Vibrational Analysis of the Negative Thermal Expansion Materials of Zn( CN) and Zn( CN) DU Zhi-yong, LIANG Er-jun , DING Pei, WANG Jun-ping, XU Er-ming ( School of Physics and E ngineering , Zhengz hou Univ er sity , Zhengz hou 450052, China) Abstract: We have classified the phonons of different symmetries in the negative thermal ex- pansion materials of Zn( CN) 2 and Cd( CN) 2 based on group theoretical analyses and calculated the Brillouin zone center phonon frequencies and corresponding Gr™neisen parameters by the first-principles plane-w ave pseudopotential method based on density functional theory. Each mode is assigned according to the eigenvector analysis and the mechanism of negative thermal expansion is explained based on Gr™neisen parameter calculations. There are 5 translational, 3 librational and 2 internal ( stretching) modes of the C S N units and 1 lattice mode of metal ions. Among these modes, 7 are Raman active, 4 are infrared active and 2 are both Raman and infrared inactive. The lowest 3 translational and all librational modes have negative Gr™neisen parameters, responsible for the negative thermal expansion. However, the low est phonon mode