Rawal, Ritesh, McQueen, Andrew J., Gillie, Lisa .J., Hyatt, Neil C., McCabe, Emma E., Samara, Kumaravinothan, Alford, Neil McN., Feteira, Antonio, Reaney, Ian M. and Sinclair, Derek C. (2009) Influence of octahedral tilting on the microwave dielectric properties of A[sub 3]LaNb[sub 3]O[sub 12] hexagonal perovskites (A=Ba, Sr). Applied Physics Letters, 94 (19). p. 192904. ISSN 00036951

Rietveld refinement of room temperature (RT) neutron diffraction (ND) data reveals 12R-type hexagonal perovskites Ba3LaNb3O12 (BLN) and Sr3LaNb3O12 (SLN) to adopt space group R with tilted NbO6 octahedra. The presence of an octahedral tilt transition (Ttilt) at 465 K in BLN from R to Rm is proposed from a combination of high temperature ND data and fixed frequency permittivity measurements. Ttilt is estimated to be much higher at ~720 K for SLN. The large difference in the RT temperature coefficient of the resonant frequency (f), −100 ppm/K for BLN compared to −5 ppm/K for SLN, is attributed to the closer proximity of Ttilt to RT for BLN. f in these 12R-type hexagonal perovskites can therefore be tuned by controlling the tolerance factor and therefore Ttilt in a manner similar to that used for many Ba- and Sr-based 3C-type ABO3 perovskites.

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