Аномальное поведение упругих свойств кристалла флюорита кальция вызванное примесью никеля

Abstract

We report the results of ultrasound studies in the CaF 2 crystal containing the low concentration impurity of nickel. We observed anomaly peaks of the elastic modulus in the temperature dependence of attenuation of ultrasound at frequency 20-55 MHz for the shear wave propagating along the [100] direction and anomalous softening of the elastic modulus c44 in the temperature interval 40-60 K. For the longitudinal mode propagating along the [100] direction the peak of attenuation and the softening of the elastic modulus c11 did not appear. We show that these anomalies are due to the ultrasound relaxation by the system of noninteraction Ni2+ Jahn-Teller centers with the 3T1 ground orbital state.