Synthesis of nitrogen and lanthanum codoped barium titanate with a novel thermal ammonolysis reactor

Abstract Lanthanum doped barium titanate was nitridated by thermal ammonolysis with a newly designed reactor, which performs extended efficiency to supply ammonia with less decomposition at elevated temperatures above 600 °C. The kinetics of nitrogen-uptake was studied systematically at elevated temperatures. Nitrogen-content, thermal stability and crystallographic phase of nitridated lanthanum doped barium titanate were characterized by several techniques. The final nitrogen-content of nitridated lanthanum doped barium titanate was much higher than the content of lanthanum, resulting in the formation of oxygen vacancies compensating the additional negative electrical charge of nitrogen anions occupying regular oxygen sites in the lattice. Through thermal ammonolysis, strongly reducing conditions because of the decomposition of ammonia generating hydrogen gas causes the formation of barium orthotitanate as a secondary phase. Ammonolysis temperature below 800 °C and suppression of thermal decomposition of ammonia gas are essential to realize a nitridated lanthanum doped barium titanate as a single phase.