Hydrothermal synthesis of potassium–sodium niobate powders

Abstract

Potassium–sodium niobates (KxNa1−xNbO3, 0 < x < 1, KNN) were hydrothermally synthesized under varying alkaline ratios (K+/Na+), total hydroxide concentration, reaction temperature, and time. Compositional surveys were developed by using Rietveld analyses derived quantitative volume fractions. The data demonstrated that phase pure KNN synthesis can be achieved by reacting the niobium source with the hydroxide solution having 6 M total hydroxide concentration, cation ratio (K+/Na+) of above 6 at temperatures ≥200°C for 24 h. Dissolution–precipitation events through intermediate products including hexaniobates were postulated as a plausible formation mechanism. It was shown also that the single‐phase KNN approaching the morphotropic phase boundary (MPB) could be obtained by further incorporation of sodium ions into the crystal via post‐annealing at 800°C/2 h, following the hydrothermal synthesis.

Open Science Research XII

“…A substituição da água pelo etilenoglicol no meio reacional, gera materiais deficientes em oxigênio já que a cinética de transferência de oxigênio do etilenoglicol é muito mais lenta que a da água. Dessa forma, materiais com diferentes propriedades eletrônicas e estruturais podem ser obtidos pela mudança na composição do solvente no tratamento solvo/hidrotérmico Piskin et al (2022). promoveram o crescimento hidrotérmico de niobatos de potássio--sódio K x Na 1−x NbO 3 (KNN) alterando sistematicamente a razão alcalina (K + /Na + ) entre 2 e 10, concentração de hidróxido entre 2 e 10 M e temperatura do meio reacional de 160 °C a 240 °C.…”