不掺杂TiO_2陶瓷的缺陷化学与气孔形成机理

Defect chemistry and formation mechanism of pores in undoped TiO_2 ceramics

通过应用缺陷化学和材料检测手段对不掺杂TiO2陶瓷气孔形成的机理进行研究。以锐钛矿TiO2粉体为原料,采用传统电子陶瓷工艺制备了不掺杂TiO2陶瓷,应用SEM、EDS和XPS测试在1 300、1 350和1 400℃烧结的不掺杂TiO2陶瓷样品的显微结构、化学组成和离子价态;根据不掺杂TiO2陶瓷晶粒的缺陷化学方程式和电中性条件,计算TiO2晶粒的缺陷浓度;基于点缺陷热力学方法,计算不掺杂TiO2陶瓷晶界的氧空位分布。结果表明:随烧结温度的升高,颗粒间的气孔逐渐减小,而晶粒中的气孔则逐渐长大,这是由于氧空位浓度随温度的增加而增加引起的。不掺杂TiO2陶瓷的氧空位在晶界出现偏析行为,并随烧结温度的增加,晶粒中的氧空位浓度和晶界氧空位浓度均随之增加。不掺杂TiO2陶瓷中存在三价钛离子和晶界吸附氧,三价钛离子浓度和晶界吸附氧含量随烧结温度的增加而增加。不掺杂TiO2陶瓷晶粒和晶界中存在较多气孔,主要起源于高温烧结过程中晶格氧的挥发和氧空位在晶界的偏析。

The formation mechanism of pores in undoped TiO2 ceramics were investigated through defects chemistry and materials testing methods.The undoped TiO2 ceramics samples were prepared from anatase TiO2 powders by traditional solid-state sintering method.The microstructure,chemistry composition and ionic valence of undoped TiO2 ceramics sintered at 1300,1350 and 1400℃ were tested by SEM,EDS and XPS.According to the defects chemistry formula and electric neutrality conditions of undoped TiO2 grains,the defects concentration in grains were calculated.Based on the point defects thermodynamic method,the oxygen vacancy distribution at the grain boundaries were obtained.The results show that the gas holes among grains reduce in scale while the pores in grain grow up with rising sintering temperature.The oxygen vacancies in undoped TiO2 ceramics segregate at grain boundaries.With increasing the sintering temperature,the oxygen vacancy concentration of both grains and grain boundaries increase.There exist trivalence Ti3＋ and grain boundaries absorbed oxygen in undoped TiO2 ceramics samples.Both absorbed oxygen content in grain boundaries and Ti3＋ concentration increase with increasing sintering temperature.There are much pores in grains and grain boundaries of undoped TiO2 ceramics samples.The pores are mainly originated from the lattice oxygen volatilization and oxygen vacancies segregation at grain boundaries during high-temperature sintering.