Pressure-induced quenching of planar rattling in Cu_(10)Zn_2Sb_4S_(13) studied by specific heat and x-ray diffraction measurements

摘要

We have studied the pressure effect on the rattling of tetrahedrite Cu_(10)Zn_2Sb_4S_(13) (CZSS) and type-I clathrate Ba_8Ga_(16)Sn_(30) (BGS) by specific heat and x-ray diffraction measurements. By applying pressure P, the rattling energy for CZSS initially decreases and steeply increases for P > 1 GPa. By contrast, the energy for BGS increases monotonically with P up to 6.5 GPa. An analysis of the pressure-dependent specific heat and x-ray diffraction indicates that the out-of-plane rattling of the Cu atoms in the S_3 triangle of CZSS originates from the chemical pressure, unlike the rattling of the Ba ions among off-center sites in an oversized cage of BGS. The rattling in CZSS ceases upon further increasing P above 2 GPa, suggesting that Cu atoms escape away from the S_3 triangle plane.