Formation of nano-sized oxides in the K-Ta-O system by chemical reaction of Ta metal with KNO3–KOH melts

Abstract

The reaction of Ta metal with potassium nitrate melts at 600 o C has been studied. It was established that the composition of the reaction product could be varied by an appropriate choice of the base-acid properties of the melt, which were regulated by additions of potassium hydroxide. Pure potassium metatantalate KTaO 3 is formed when the KOH/KNO 3 molar ratio is about 1.2 or slightly higher. A mixture of the metatantalate with tetra-and ditantalate (K 2 Ta 4 O 11 and K 2 Ta 2 O 6) is formed at lower molar ratios. The content of tetratantalate increases as the concentration of KOH in the melt decreases and it becomes the main reaction product in pure nitrate melt. Pure metatantalate was obtained in the form of powders with grain sizes of about 80 nm. This product possessed ferroelectric properties with a dielectric constant of 250-300. Such nano-powders exhibit the properties of a semiconductor, which is not common for large-crystal materials. The conductivity is 10-5 S cm-1 at room temperature and increases exponentially with increasing temperature.

Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3

“…The synthesis procedure is described in detail in Ref. [21]. After synthesis, the powder was additionally annealed at 1000 K in the air for 1.5 h to remove the residual moisture.…”

“…Recently, Andriiko's group synthesized a nanocrystalline potassium tantalate with particles of 70-90 nm in diameter. 21 Ceramic samples were made from this powder, and some interesting effects were observed. 22 Firstly, a wide peak at 20-30 K was observed in the temperature dependence of dielectric constant.…”