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Structural study of Cr-doped barium aluminate

Barium aluminate, BaAl2O4, is a widely used material that has a high technological application in the field of electronics and optical communications.1 Specially, it has been extensively investigated as a promising host for long afterglow luminescent materials. Namely, when doped/co-doped with transition metal cations or rare earth cations, barium aluminate exhibits good luminescence properties.2, 3 Chromium is a low cost activator, and Cr3+-doped systems are already used in modern technologies, for example in production of solid-state lasers. Barium aluminate possesses a stuffed tridymite structure with barium cations incorporated into channels inside a three-dimensional network of corner sharing AlO4 tetrahedra.4 It exists in two hexagonal phases which are reversibile at 123 °C. At room temperature a ferroelectric phase in P63 space group is present, while at high temperature a paraelectric phase in P6322 space group is observed.5 Powder samples of barium aluminate doped with 0-12 at.% Cr were prepared by a hydrothermal method and additionally annealed at 900 °C for 4 h. Prepared samples were characterized by X-ray diffraction at RT, and their crystal structures were refined by the Rietveld method, simultaneously with the analysis of diffraction line broadening. The XRD patterns showed that all samples had the hexagonal stuffed trydimite structure in space group P63. The unit-cell parameters were precisely determined using silicon powder as an internal standard, and refined by the WPPF program.6 EPR and photoluminescence measurements indicated that chromium was present as Cr3+ ion in the doped samples. Rietveld refinement showed in which sites of BaAl2O4 structure Cr3+ dopant cations are incorporated. Line broadening analysis revealed that samples contained crystallites of ~30 nm in size. References: 1 C. Kim, I. Kwon, C. Park, Y. Hwang, H. Bae, B. Yu, C. Pyun, G. Hong, J. Alloys and Compd., 2000, 311, 33. 2 K. Fukuda, T. Iwata, T. Orito, J. Solid State Chem., 2005, 178, 3662. 3 Y. Lin, Z. Zhang, Z. Tang, J. Zhang, Z. Zheng, X. Lu, Mater. Chem. Phys., 2001, 70, 156. 4 A. Putnis, An Introduction to Mineral Sciences, Cambridge University Press, 1992. 5 S.-Y. Huang, R. Von der Muell, J. Ravez, J. P. Chaminade, P. Hagenmuller, M. Couzi, J. Solid State Chem., 1994, 109, 97. 6 H. Toraya, J. Appl. Crystallogr., 1986, 19, 440.

hydrothermal method; powder diffraction; Rietveld structure refinement; size-strain analysis

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