Investigations on temperature dependences of parameters of ¹²⁷I NQR spectrum of (BiI₃)(₁₋ₓ)(PbI₂)ₓ mixed layered semiconductor and alkaline halogens crystals

Abstract

Results of investigations of the temperature dependence of NQR frequencies in the temperature range of 4.2-150 K for ¹²⁷I and ⁷⁹Br of the (BiI₃)(₁₋ₓ)(PbI₂)ₓ mixed layered semiconductor and the crystals of alkaline halogens are presented. The abnormally large absolute values of temperature coefficients of the NQR frequency for (BiI₃)(₁₋ₓ)(PbI₂)ₓ have been detected. It can be explained by influence of the point charges and interlayer fluctuations. It is concluded that the quasi-two-dimensional nature of the vibration states at PbI₂ contents of x ≤0.08 is persistent. The value of the orientation and translational vibrations frequency of the halogen ions assuming the correctness of the two-frequency model Bayer-Kushida has been calculated.