Effect of La Content on the Thermal Volume Change of Ba 4.22 Na 1.44 Nb 10.12 O 30.24 -Ba 3 NaLaNb 10 O 30 Solid Solutions at Ferroelectric Transition Temperature

Sintered solid solutions in the Ba 4.22 Na 1.44 Nb 10.12 O 30.24 (BNN-B)-Ba 3 NaLaNb 10 O 30 (BNLN) system have been synthesized and examined by X-ray powder diffraction and differential scanning calorimeter (DSC) analysis. The BNN(-B)-BNLN system has continuous solid solutions over the whole range, which have a tungsten bronze type of structure with pseudotetragonal symmetry. At room temperature, the a -axis increases slightly with increasing La content while the c -axis markedly decreases. The temperature dependence of the axes is characteristic in the c -axis. The thermal contraction of the c -axis occurring at the ferroelectric transition temperature is depressed with increasing La content, and in an intermediate composition, the contraction is reduced to nearly zero. The DSC analysis showed that both the transition enthalpy (Δ H t ) and the transition temperature ( T t ) decrease with increasing La content.