Influence of octahedral tilting on the microwave dielectric properties of A3LaNb3O12 hexagonal perovskites (A=Ba, Sr)

Rawal, Ritesh; McQueen, Andrew J.; Gillie, Lisa J.; Hyatt, Neil C.; McCabe, Emma E.; Samara, Kumaravinothan; Alford, Neil McN.; Feteira, Antonio; Reaney, Ian M.; Sinclair, Derek C.
May 2009
Applied Physics Letters;5/11/2009, Vol. 94 Issue 19, p192904
Academic Journal
Rietveld refinement of room temperature (RT) neutron diffraction (ND) data reveals 12R-type hexagonal perovskites Ba3LaNb3O12 (BLN) and Sr3LaNb3O12 (SLN) to adopt space group R3 with tilted NbO6 octahedra. The presence of an octahedral tilt transition (Ttilt) at 465 K in BLN from R3 to R3m 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 (τf), -100 ppm/K for BLN compared to -5 ppm/K for SLN, is attributed to the closer proximity of Ttilt to RT for BLN. τf 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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