Study of Dielectric Properties of Nano-scale Thin Films of Dielectric Materials

为了获得微观介电相互作用对介电材料宏观介电性能影响的信息，研究了铁电和反铁电材料固溶体系统中铁电和反铁电性之间的受挫效应所实现的偶极玻璃态的热学和介电性质。在此基础上，研究了射频溅射法在石英玻璃衬底上制备的典型铁电材料BaTiO_3和具有量子顺电性质的SrTiO_3薄膜的结构和介电性能，阐明了介电相互作用区的大小与宏观介电性能的关系。结果如下：1.用绝热量热法成功地测定了PYH(BF_4)_x&lt；1-x&Gt；(PF_6)_x(Py=C_5NH_5)固溶体体系的偶极玻璃化转变。这是第一次用量热法观察到偶极-玻璃转变，这一结果有力地表明，偶极-玻璃态本质上是由于重定向速度随着温度的降低而减慢而导致的偶极子构型的冻结非平衡状态。2.在溅射成膜过程中，通过改变石英玻璃衬底的温度，BaTiO_3和SrTiO_3薄膜中形成的微晶尺寸分别控制在30和40 nm。在200~300K温度范围内，薄膜样品的介电常数随晶粒尺寸的增大而增大，表现出与块体不同的立方晶系结构。

In order to obtain the information about the effect of microscopic dielectric interactions to the macroscopic dielectric properties of dielectric materials, thermal and dielectric properties were investigated of the dipolar-glassy state, which was realized by the frustration effect between ferroelectricity and antiferroelectricity in the solid-solution systems of ferroelectric and antiferroelectric materials. Further, the structures and dielectric properties of thin films of BaTiO_3, which is a typical ferroelectric material, and of SrTiO_3, which shows a quantum paraelectric property, formed on quartz glass substrate by RF sputtering method were studied to elucidate the correlation between the size of dielectric interaction region and the macroscopic dielectric properties. The results are as follows :1.The dipolar-glass transition in the solid-solution system of PyH(BF_4)_<1-x>(PF_6)_x (Py = C_5NH_5) was detected successfully by an adiabatic calorimetry as a glass transition. This is the first case where the dipolar-glass transition was observed calorimetrically, and the result strongly suggests that the dipolar-glassy state is, in essence, a frozen-in non-equilibrium state of the configuration of dipoles due to slowing down of the reorientation rate with decreasing temperature.2.The grain sizes of crystallites formed in the thin films of BaTiO_3 and SrTiO_3 were found to be controlled up to 30 and 40 nm for BaTiO_3 and SrTiO_3, respectively, by changing the temperature of the quartz glass substrate during the film formation by the sputtering method. The crystallites of BaTiO_3 with the nm-grain size showed the crystal structure belonging to cubic crystal system differently from the bulk, and the dielectric permittivity of the film samples was observed to become larger with the increase of the grain size in the temperature range between 200 and 300 K.