Study On Flash Sintering Behavior At Low Temperature Of Co-and Ca-Doped LaCrO₃

Lanthanum chromate-based ceramic material is a widely used functional ceramic material,and its performance in all aspects can be further improved by doping modification.However,Doped lanthanum chromate are difficult to be densified during the sintering process,in which the required sintering temperature is high,the holding time is long,and there is the volatilization of Cr.In view of the difficulty of sintering doped lanthanum chromate,researchers mostly start with improving the sintering characteristics of the powder and adopting new sintering methods to quickly prepare densified doped lanthanum chromate at low temperature.Flash sintering is a sintering technology that has emerged in recent years.Because of its low sintering temperature,short sintering time,fast heating rate,and low energy loss,it is favored by researchers.The purpose of this article is to achieve low-temperature rapid densification of lanthanum chromate ceramics through flash sintering technology,and to study the effect of doping on flash sintering behavior,and then to discuss the contribution of defects in the flash sintering process.Doped lanthanum chromate powders were synthesized by the sol-gel method.Firstly study the flash sintering behavior of Co single-doped lanthanum chromate materials.The electric field strength was 10-60V/cm,and the current density exhibited different laws with the increase of temperature.Above the threshold electric field,as the applied electric field strength increased,the onset temperature of flash sintering decreased accordingly.And investigate the effects of current density and holding time on the microstructure of the flash sintering samples.For example,LaCr_0.8Co_0.2O₃,when the electric field strength was 40V/cm,the current density was limited to 60A/cm²,the average particle size of lanthanum chromate prepared after flash sintering for 100s was much smaller than that of conventional sintering,and the density is significantly improved.Simultaneously,the effect and reason of cobalt ion doping at the B site on the conditions of flash sintering were analyzed.Studies have shown that with the increase of cobalt doping content,the threshold electric field decreases,and the onset temperature of flash sintering under the same electric field intensity also decreases.According to the relationship between the electric field strength and the onset temperature,the activation energy value of the material in flash sintering were obtained by the linear fitting.The activation energy value decreases with the increase of the cobalt doping amount,and the corresponding power loss value also shows a decreasing trend.This is consistent with the change of the threshold electric field.That is,the threshold condition decreases with the increase of cobalt doping,and this rule is matched.In order to analyze the internal reasons,by characterizing the characteristics of the powder material,it is obtained that the band gap value decreases with the increase of cobalt doping.This is caused by the increase of the carrier concentration caused by the doping of Co ions.After the partial substitution of Co²⁺for Cr³⁺,the appearance of Co³⁺and the decrease of Cr³⁺content and the increase of Cr⁶⁺content,at the same time,the lattice oxygen content decreases,resulting in an increase in oxygen vacancies.The existence of the above-mentioned charging defects such as holes and oxygen vacancies promotes the occurrence of the flash sintering under lower threshold conditions.On this basis,the flash sintering behavior of calcium and cobalt co-doped lanthanum chromate(La_0.9Ca_0.1Cr_0.8Co_0.2O₃)was studied.Partial replacement of La³⁺by low-priced Ca²⁺leads to a further increase in the concentration of Cr⁶⁺,that is,the number of oxygen vacancies is higher than La_0.9Ca_0.1Cr_0.8Co_0.2O₃.At the same time,the band gap value is lower than La_0.9Ca_0.1Cr_0.8Co_0.2O₃,which corresponds to the phenomenon that the threshold condition of double doping in the experiment is lower than that of single doping with Co.Experimentsshow that the threshold electric field strength of La_0.9Ca_0.1Cr_0.8Co_0.2O₃is lower.When the electric field strength is greater than 15V/cm,the flash sintering process can occur at room temperature.