Crystal structure of tricalcium tantalum trigallium disilicon oxide, Ca3TaGa3Si2O14

Abstract

Source of materialCa3TaGa3SÌ20i4 (CTGS) was prepared by solid-state reaction of a stoichiometric mixture of 99.99% CaCC>3, Ta2Ü5, SiCb and 98% Ga2Ù3 powders. The powders were ground, mixed for 12 h and pressed into tablets. The latter were heated at 1373 Κ for 6 h to decompose CaCC>3 completely and produced CTGS ceramics. The ceramic materials were put into an Ir crucible and melted by RF-heating using an atmosphere of pure nitrogen plus a small amount of oxygen in order to avoid the evaporation of gallium suboxide from the melt during growth. The crystal pulling and rotation rates were 1-3 mm/h and 15-30 rpm, respectively. When the length of the crystal was sufficient, the temperature was lowered to room temperature at a rate of 30-180 K/h. The colorless and transparent single crystals of CTGS (16-14 mm in diameter and 37 mm in length) suitable for X-ray structure analysis were obtained. DiscussionIn the structure of Ca3TaGa3SÌ20u, the Ca-O bond lengths in the Ca0 8 dodecahedra are 2.363 (3) (1)°) are larger than the remaining (103.9(2)°), which are slightly different from the ideal value for a tetrahedron. From the above discussion, it is clear that the CaOs, TaOô, GaÜ4 and S1O4 polyhedra of the CTGS structure are all distorted, which leads to a high efficiency of second harmonic generation (SHG) in CTGS crystals. The distortion of polyhedra in CTGS crystal is somewhat higher than that of the Ca3NbGa3Si20i4 crystals [2], the more polyhedrons distortion, the higher the SHG efficiency. The SHG efficiency was studied by the powder technique and emission of a strong green light (532 nm) was observed, with an intensity weaker than that generated by LiNbC>3 and La3GasSiOi4 crystals but stronger than that obtained from Ca 3 NbGa3SÍ20i 4 crystals.

Оптические свойства кристаллов семейства лангасита: La-=SUB=-3-=/SUB=-Ga-=SUB=-5-=/SUB=-SiO-=SUB=-14-=/SUB=-, La-=SUB=-3-=/SUB=-Ga-=SUB=-5.5-=/SUB=-Ta-=SUB=-0.5-=/SUB=-O-=SUB=-14-=/SUB=-, Ca-=SUB=-3-=/SUB=-TaGa-=SUB=-3-=/SUB=-Si-=SUB=-2-=/SUB=-O-=SUB=-14-=/SUB=-

“…В соединении LGS тетраэдрические позиции D статистически заполняются ионами кремния и галлия [8,9], в CTGS ионы элементов занимают в структуре предназначенные им позиции [14]. Относительно заполняемости позиций в LGT сведения, представленные в литературе, разнятся: в работе [12] показано, что все ионы занимают свои позиции в структуре, а в работах [8,13] показано, что ионы галлия могут занимать не только тетраэдрические позиции, но и октаэдрические позиции B. В силу заполнения позиций соединения CTGS относят к упорядоченным кристаллам, а LGS и LGT -к разупорядоченным.…”