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The Effect of Hydrothermal Synthesis Parameters on the Formation of Sodium Bismuth Titanate

ABSTRACT We report the effect of various Bi:Ti ratios x:1 (x = 0.5–3) on the phase formation of sodium-bismuth titanate Na0.5Bi0.5TiO3 (NBT) during hydrothermal synthesis (230°С, 3 MPa, 96 h) from titanium oxide and bismuth hydroxide in 20 M NaOH solution. It was shown that single-phase ceramics with perovskite structure could be obtained at x = 0.5–0.9 using the hot-pressing technique (1025°С, 60 MPa, 1 h). At x = 1, hydrothermal synthesis results in single-phase samples, while, after sintering, the admixture of Na2Ti3O7 was detected. At x = 2 and 3, samples contained admixtures after hydrothermal synthesis. The x–value does not significantly affect the composition of perovskite-like products despite the excess of bismuth in the system. The chemical composition of the samples with x = 0.5–0.9 corresponds to the general formula Na0.60–0.69Bi0.40–0.31TiO2.9–2.81δ0.10–0.19 (where δ represents vacancies in oxygen sublattice). The Bi3+ content in the samples is underestimated due to the solubility of its hydroxide in a 20 M alkali solution. The properties of ceramics are not significantly affected by x values, and materials exhibit following average characteristics: electrical resistivity 1.3 × 109 Ohm∙cm, tanδ = 0.15, Кр = 0.1, d31 = 6.7 and d33 = 9.5 pC/N, g31 = 2.34 and g33 = 3 mV∙m/N.