Abstract Single crystals of ABW-type CsAlTiO4 (CAT), CsFeTiO4 (CFT), CsGaTiO4 (CGT), and ANA-type CsTi1.1Si1.9O6.5 (CST) were grown and characterized by electron microprobe analyses, single-crystal X-ray diffraction, thermal analyses, and spindle-stage optical investigations to determine the electronic polarizability of 4-coordinated Ti4+, α([4]Ti4+). The crystal structure of CAT was confirmed to crystallize in the highest possible topological symmetry Imma (a = 8.9677(2) Å, b = 5.7322(1) Å, c = 9.9612(3) Å) with tetrahedrally coordinated Al and Ti equally distributed on Wyckoff position 8i. Twinning by reticular merohedry with a twin index of 2 was observed for most of the crystals resulting in a hexagonal twin lattice (a = 11.487(3) Å, c = 8.968(2) Å) with Laue symmetry 6/mmm. Refractive indices measured by immersion methods on an untwinned specimen are n x = 1.716(5), n y = 1.725(2), and n z = 1.727(1) with 2V z = 127.1(6)°. The diffraction patterns of CFT and CGT clearly showed superstructure reflections causing a symmetry lowering of index 4 with a transformation according to 2a, b, c from Imma to Pmab with a = 18.3054(7) Å, b = 5.8083(2) Å, c = 9.9938(4) Å for CFT, and a = 18.2921(6) Å, b = 5.7636(2) Å, c = 9.9210(3) Å for CGT. Refractive indices for CGT are n x = 1.750(3), n y = 1.772(3), and n z = 1.776(2) with 2V z = 132(1)°. The crystal structure of the ANA-type CsTi1.1Si1.9O6.5 was confirmed to crystallize in space group Ia 3 ¯ $\overline{3}$ d (a = 13.8333(4) Å). The extra 0.5 O atoms are needed for charge compensation and to allow the sum of electronic polarizabilities to give a total electronic polarizability calculated from the refractive index n = 1.718(4). The electronic polarizability of [4]Ti4+ was calculated from the difference between the observed total polarizabilities (derived from the mean refractive indices of CAT and CGT) and the sum of electronic polarizabilities of cations and anions omitting the polarizability of Ti resulting in α([4]Ti4+) = 5.15(5) Å3.

中文翻译：

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ABW 型 CsMTiO4（M = Al、Fe、Ga）和 ANA 型 CsTi1.10Si1.90O6.50 的合成、修正晶体结构和折射率，以及 4 配位 Ti4+ 的电子极化率的测定

摘要 ABW 型 CsAlTiO4 (CAT)、CsFeTiO4 (CFT)、CsGaTiO4 (CGT) 和 ANA 型 CsTi1.1Si1.9O6.5 (CST) 的单晶生长并通过电子探针分析、单晶 X-射线衍射、热分析和主轴级光学研究，以确定 4 配位 Ti4+，α([4]Ti4+) 的电子极化率。CAT 的晶体结构被证实以最高可能的拓扑对称性 Imma（a = 8.9677(2) Å, b = 5.7322(1) Å, c = 9.9612(3) Å）结晶，四面体配位的 Al 和 Ti 均匀分布在威科夫位置 8i。对于大多数晶体，观察到孪晶指数为 2 的网状多面体孪晶导致六方孪晶晶格（a = 11.487(3) Å，c = 8.968(2) Å），劳厄对称性为 6/mmm。在非孪晶试样上通过浸入法测量的折射率为 nx = 1.716(5)、ny = 1.725(2) 和 nz = 1.727(1)，2V z = 127.1(6)°。CFT 和 CGT 的衍射图清楚地显示超结构反射导致指数 4 的对称性降低，根据 2a、b、c 从 Imma 到 Pmab 的转换，a = 18.3054(7) Å, b = 5.8083(2) Å, c CFT = 9.9938(4) Å，CGT 为 a = 18.2921(6) Å，b = 5.7636(2) Å，c = 9.9210(3) Å。CGT 的折射率为 nx = 1.750(3)、ny = 1.772(3) 和 nz = 1.776(2)，其中 2V z = 132(1)°。ANA 型 CsTi1.1Si1.9O6.5 的晶体结构被证实在空间群 Ia 3 ¯ $\overline{3}$ d (a = 13.8333(4) Å) 中结晶。额外的0。需要 5 个 O 原子来进行电荷补偿并允许电子极化率的总和给出根据折射率 n = 1.718(4) 计算的总电子极化率。[4]Ti4+ 的电子极化率是根据观察到的总极化率（源自 CAT 和 CGT 的平均折射率）与忽略 Ti 极化率的阳离子和阴离子的电子极化率之和之间的差异计算得出的，从而得到 α([ 4]Ti4+) = 5.15(5) Å3。