X-ray diffraction study of La3Ga5.5Ta0.5O14 and La3Ga5.5Nb0.5O14 langasite-type single crystals
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- Kuz’micheva, G.M., Tyunina, E.A., Domoroshchina, E.N. et al. Inorg Mater (2005) 41: 412. doi:10.1007/s10789-005-0145-6
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The structure of langatate (as-grown and vacuum-annealed: LGT-I and LGT-II, respectively) and langanite (seed- and tail-end portions: LGN-III and LGN-IV, respectively) single crystals grown by the Czochralski technique from charges of nominal composition La3Ga5.5M0.5O14 = La3(Ga0.5M0.5)(1)Ga3(2)Ga2(3)O14 (M=Ta5+, Nb5+) is studied by x-ray diffraction. The LGT-I and LGT-II crystals are shown to differ in the Ga and Ta distributions over crystallographic sites: La3(Ga0.52)Ta0.48(2)5+Ga3(Ga0.94Ta0.06(1)3+)2O14 in LGT-I (Ta5+ in the octahedral site Ga(1) and Ta3+ in the trigonal-pyramidal site Ga(3)) and La3(Ga0.55Ta0.45(2)5+)Ga3Ga2O13.93(2)□0.07 in LGT-II (Ta5+ in the octahedral site Ga(1) and oxygen vacancies in O(1)). The increased Ta content is responsible for the lower structural perfection of LGT-I. LGN-III and LGN-IV have essentially identical compositions, La3(Ga0.47Nb0.53(1)5+)Ga5O14 and La3(Ga0.48Nb0.52(1)5+)Ga5O14, respectively, but differ in polarity.