Reactions of the Group VB Pentoxides with Alkali Oxides and Carbonates. III. Thermal and X-Ray Phase Diagrams of the System K₂O or K₂CO₃ with Ta₂O₅

Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate

“…12 To account for these two possible modes of proton incorporation and the cation vacancies that likely accompany hydroxyl group formation, [13][14][15][16] the chemical formula of potassium tantalate hydrate may be written as K x Ta y O 3−z (OH) z и nH 2 O, where x + 5y + z ‫ס‬ 6 is required for overall charge neutrality. The presence of cation vacancies as charge compensation defects is experimentally supported by the work of Shi and coworkers, 6 who observed by FTIR and electron paramagnetic resonance that the concentration of Ba 2+ vacancies increased with increasing OH − concentration in BaTiO 3 . Subsequent to synthesis, complete dehydration, as recorded in the TGA experiments, involves the loss of (z/2 + n) molecules of water, i.e.,…”

“…Conventional solid-state synthesis based on mixed powders requires long periods of heating at 1000°C. 6 Alternatively, when using precursors such as alkoxides, a defect pyrochlore phase, K 2 Ta 2 O 6 crystallizes at 650°C; the perovskite phase is obtained only after heating to 850°C. 7 Attempts to generate potassium tantalate powders by the hydrothermal method have, to date, produced materials with only a defect pyrochlore structure.…”

Growth of potassium tantalate (KTaO3) crystals by directional solidification

“…According to the K 2 CO 3 -Ta 2 O 5 phase diagram [5], the liquidus and solidus close to the ratio of K 2 CO 3 : Ta 2 O 5 = 50: 50 mol% (stoichiometric composition for KTaO 3 ) have not been reported precisely. Although the primary phase for the stoichiometric melt has been reported to be KTaO 3 [5], KTaO 3 has been recognized as an incongruent material.…”

“…Although the primary phase for the stoichiometric melt has been reported to be KTaO 3 [5], KTaO 3 has been recognized as an incongruent material. In fact, KTaO 3 crystal is generally grown by solution growth such as topseeded solution growth (TSSG) [1], the flux method [6] or the hydrothermal technique [7].…”

Oxidation of TaSi2-Containing ZrB2-SiC Ultra-High Temperature Materials~!2009-09-08~!2009-12-23~!2010-04-20~!

“…The expected oxidation products, SiO 2 and Ta2O5 have melting points of 1723C [5] and 1872C (a-Ta2O5) [13] respectively. Upon oxidation at temperatures above 1872C, TaSi2 is therefore expected to form a liquid phase.…”