Anomalies in Refractive Index of Pb1-xGexTe Thin Film Corresponding to Ferroelectric Phase Transition
Pb_(1-x)Ge_xTe薄膜在铁电相变点的折射率异常

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.