Dorota A. Pawlak
Institute of Electronic Materials Technology, 01-919 Warszawa, Poland
Masahiko Ito
Physical Chemistry of Luminescent Materials, Claude Bernard/
Lukasz Dobrzycki and Krzysztof Wozniak
Warsaw University, Chemistry Department, 02-093 Warszawa, Poland
Masaoki Oku
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Kiyoshi Shimamura
Advanced Materials Laboratory National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan
Tsuguo Fukuda
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
Five different mixed-perovskite (AA′)(BB′)O3 single crystals were grown, where A = La, Nd; A′ = Sr; B = Al, Ga; and B′ = Ta, Nb. The as-grown crystals were yellowish/brownish. After annealing in air, the coloration was more intense. Annealing in a reducing atmosphere decreased coloration. The crystals were investigated by transmission spectroscopy, electron spectroscopy for chemical analysis (ESCA), and single-crystal x-ray diffraction. Additional broad absorption bands in the transmission spectra were observed for the as-grown samples. They are in line with the changes of the shape of O(1s) ESCA peaks. Redundant interstitial oxygen ions were recognized as the reason for the crystal coloration. All structures were solved and refined in different space groups of their regular systems. Some of the unit cells have a doubled lattice constant: (i) LSGN, Pm3 m, 3.9323(5) Å, at 100K, 3.9270(5) Å; (ii) NSAT, Pm3 m, 3.8353(4) Å; (iii) LSAT, Pn3 m, 7.720(1) Å, annealed in reducing atmosphere, 7.708(1) Å; (iv) NSAN, Fm3 m, 7.744(4) Å.