Mn掺杂对La_(0.5)Ca_(0.5)Mn_xTi_(1-x)O_3介电行为的影响

EFFECT OF Mn DOPING ON THE DIELECTRIC BEHAVIOR OF La_(0.5)Ca_(0.5)Mn_xTi_(1-x)O_3

利用传统的固相烧结方法,成功制备了La和Ca,Mn和Ti相互替代的正交钙钛矿相La0.5Ca0.5MnxTi1-xO3(0≤x≤0.6)陶瓷。通过X射线衍射,阻抗分析仪对体系物相结构和介电性能进行了测试分析。结果表明:由于La,Ca和Mn,Ti的共存以及保持电中性的要求,该体系极易受从Mn4+转变为Mn3+的作用,在Mn含量不同时引入不同的空位缺陷,当Mn3+含量与La3+含量相当时体系中产生的缺陷相对最少,其介电常数最大,反之随两者含量偏差的增大而下降;La0.5Ca0.5MnxTi1-xO3分别在400～450℃和150～300℃之间出现2个介电峰。体系中La3+和氧空位等产生的p型载流子和Mn离子变价引入的n型载流子在外电场下发生局域重排,产生了载流子极化,并在150～300℃范围被活化。同时由于这两种载流子对温度影响的响应不同,产生了与Mn离子的掺入相关的介电峰。在400～450℃范围,体系出现了相应为正交与立方结构转变的介电峰,也即Curie点。

La0.5Ca0.5 MnxTi1-xO3 formed with the orthorhombic perovskite phase which keeps substitution each other between La and Ca as well as Mn and Ti were prepared by traditional solid state sintering process. The phase structure and dielectric behavior were measured by XRD and impedance meter. The results show that the dielectric properties of La0.5Ca0.5 MnxTi1-xO3 is easily affected by Mn3+ ion transformed from Mn4+ due to the demand of the electronic neutrality when coexisting ions of La, Ca and Mn, Ti ions together. The vacancy deficiency is formed and changed as changing the content of Mn ions in the system. If the contents of Mn3+ and La3+ are comparatively the same, the deficiency level keeps relatively the lowest and the dielectric constant however shows the highest. On the contrary, the dielectric constant decreases with the increase of the contents difference of Mn3+ and La3+. There are two dielectric peaks appear at the temperature of 400-450°C and 150-300°C respectively in the system. Both of p type-carries supplied by La3+ or oxygen hole and n type-carries induced by changing Mn4+ into Mn3+ can be locally displaced and simultaneously response with external electric field. The carrier polarization is hence generated and in fact activated in lower temperature range between 150°C and 300°C. Consequently, the dielectric peak related to the carrier polarization appears because of the different behaviors of temperature response of these two kinds of carriers at this low temperature range. On the other hand, the dielectric peak appears due to the phase transformation between orthorhombic and cubic at the higher temperature range of 400-450°C, which is in fact the Curie point.