Pb1-xGexTe薄膜在铁电相变点的折射率异常

对在80～300K温度范围测量的Pb1-xGexTe(x=0.06)薄膜透射谱采用Lorentz谐振子模型进行拟合得到折射率.研究发现:在其铁电相变温度150K折射率出现极大值.折射率的极大值是晶体电容率异常的标志,而晶体电容率异常正是晶体相变具有铁电性的反映,因此同电阻和比热一样,折射率在铁电相变点也出现了异常.在所研究的光谱及温度范围,折射率与材料的禁带宽度不遵循Moss定则等经验公式.

Anomalies in Refractive Index of Pb1-xGexTe Thin Film Corresponding to Ferroelectric Phase Transition

The refractive index n of Pb_ 1-x Ge_ x Te ( x =0.06) thin film is determined from transmission spectra measured at temperatures between 80 and 300K by fitting based on a Lorentz-oscillator model.It is found that a maximum of refractive index occurs at 150K,which is the structure phase transition temperature T _c.This maximum is identified with occurrence of abnormal permittivity that is an indication of the ferroelectric nature of the phase transition.Therefore,it can be concluded that anomalies in the refractive index,similar to those in the electrical resistivity and specific heat,occur at the phase transition from rocksalt to rhombohedrally distorted structure.The empirical relations,such as Moss relation,are not suitable to the refractive index and band gap in the range of spectrum and temperature.