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Structural Distortion and Dielectric Permittivities of KCoO2-Type Layered Nitrides Ca1-SrTiN2
Shenglin Lu1, Yanhui Wang1, Fengqi Lu1
1MOE Key Laboratory of New Processing Technology for Nonferrous Metals and Materials, Guangxi Key Laboratory of Optical and Electronic Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, P. R. China.
Abstract:
Among the KCoO2-type phases, the orthorhombic layered nitride CaTiN2 is a newly reported high dielectric permittivity material (εr ∼ 1300-2500 within 104-106 Hz from 80 to 450 K) while the tetragonal SrTiN2 is reported to display an unintentional metallic conduction property. In this work, a Ca1-SrTiN2 solid solution was synthesized, in which the insulating SrTiN2 end member and some Sr-doped CaTiN2 samples were successfully obtained, and therefore, the dielectric properties of the Ca1-SrTiN2 solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca1-SrTiN2, which reduced the dielectric permittivity significantly. The tetragonal SrTiN2 displays a much lower dielectric permittivity (εr ∼ 20-70 in 105-106 Hz and 10-300 K) than that of CaTiN2. The comparison on the dielectric permittivities and structures of CaTiN2 and SrTiN2 indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN2 pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN2.
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