La-Mn共添加チタン酸バリウムの電気的および分光学的性質に及ぼす焼成雰囲気の影響

抄録

Effect of firing atmosphere on the electrical properties of La-doped and La-Mn-codoped BaTiO₃ ceramics was studied by combining diffuse reflectance measurements and electron spin resonance (ESR) spectroscopy The room temperature resistivity of 0.2mo%La-0.05mol%Mn-codped and 0.3mol%La-0.05mol%Mn-codoped samples fired in air was lower than that of La-doped samples. The result attributed to promotion of grain growth by addition of Mn. The room temperature resistivity of the samples fired in Ar was independent on the concentration of La and Mn, and was inclined to be lower than that of samples fired in air. It was assumed that oxygen vacancies were formed in the samples fired in Ar and resulted in generation of conduction electrons. All samples prepared in this study were semiconductive and the behavior of absorbance in the range of near infra-red agreed with the relationship between electron conductivity and La concentration. The result suggested that the intensity of absorbance was due to the concentration of conduction electrons. The decrease of positive temperature coefficient of resistivity of La-Mn-codoped samples fired in Ar was assumed to cause by decrease of chemisorbed oxygen in the grain boundary region. The line width of the ESR signal of Mn²⁺ observed in the sample fired in Ar was larger than that in the samples fired in air. The result indicated that part of Mn³⁺ in the grain boundary region was reduced to Mn²⁺ during firing in Ar.