Dielectric Function of Superionic Material AgI in the Molten and alpha Phase

(1)首先，我们研究了碘化银在α（超离子）和熔融相的动力学结构因素。电荷密度相关函数S_<CC>（kappa，omega）在15 ps ~（-1）处只有一个宽峰<-1>。这些都是从偏动力学结构因子S_<II>（kappa，omega）S_<AgAg>（kappa，omega）得到的。在<II>α相中，S_（kappa，omega）的LO模的尖峰在熔融相中变得非常宽。S_<II>（kappa，omega）在熔融相中的行为与S_<AgAg>（kappa，omega）相似。在熔融相中，S_<II>（kappa，omega）的LO模峰变宽，LO模不明显。(2)然后用S_（kappa）计算了碘化银的静态介电函数ε_（kappa<CC>）。当接近熔融温度时，在某些kappa值处，λ（kappa）与横坐标轴接触。这表明熔融相中的离子倾向于与固相类似地有序化。在α相中，在特定波数处，λ（kappa）的值变为零，这导致德拜峰。在经典的单组分等离子体和氢等离子体中发现了非常相似的行为。对epsilon（kappa）的研究为我们提供了有关规则晶格系统中离子有序的信息，以及从液态有序的先导现象的迹象。(3)本文提出了一个描述阳离子快离子导体低能激发模式的离子等离子体模型。当考虑阳离子的有效电荷时，该模型得到了实验的支持。

(1) First we have studied the dynamical structure factors of AgI in the alpha(superionic) and molten phases. The charge-density correlation function S_<CC>(kappa,omega) has only a broad peak at about 15 ps^<-1>. These things have been understood from the partial dynamical structure factors S_<II>(kappa,omega) S_<AgAg>(kappa,omega). The sharp peak of the LO mode in S_<II>(kappa,omega) in the alpha-phase becomes extremely broad in the molten phase. The behavior of S_<II>(kappa,omega) in the molten phase is similar to that of S_<AgAg>(kappa,omega). The peaks of the LO mode in S_<II>(kappa,omega) become broad and then the LO mode does not appear clearly in the molten phase.(2) Next we have calculated the static dielectric function epsilon(kappa) of AgI using S_<CC>(kappa). The epsilon(kappa) touched the abscissa axis at some values of kappa as the melting temperature was approached. This shows the tendency of ions in the molten phase to order similarly to the solid phase. In the alpha-phase, the values of epsilon(kappa) became zero at special wave numbers which lead to the Debye peaks. Very similar behavior was found in a classical one-component plasma, and a hydrogen plasma. The study of epsilon(kappa) gave us information about ordering of ions in a regular lattice system and a sign of the forerunning phenomena to an ordering from a liquid state.(3) We have presented an ionic plasma model to describe the low-energy excitation mode in cation superionic conductors. When taking account of an effective charge of cations, the model is supported by experiments.