中文摘要：

无铅弛豫铁电体具有较好的介电可调性，在顺电相有较大的介电常数和极小的损耗，因较大的优值而被广泛地用于微波器件．根据现有的介电可调性理论，通过参量的适当修正。对介电可调性的表达式做了合理的探讨，结论适用于处理实验结果．比较发现，在电场作用下顺电相保持不变的近似得出的结论与实验结果差距较大，而转化为铁电相与实验结果完全吻合．考虑外加电场和自发极化对弹性吉布斯自由能的修正，导出了高电场对介电常数的修正关系，与实验结果相符．提出了介电可调度的概念与计算公式，能够定量表示掺杂对介电可调性的影响．

英文摘要：

Based on the high dielectric tunability, high dielectric constant and small dielectric loss at paraelectric phase, lead-free relaxor ferroelectrics have been used in microwave devises widely. According to the present theory of dielectric tunability, the expression of dielectric tunability is derived by adjusting parameters properly. The derived expression can be used to deal with experimental results. It is found that there exists a great difference between experimental result and the theoretical result obtained under the assumption of unchanged paraelectric phase under an electric field, while the experimental result and the theoretical result of Johnson in 1962 is consistent. A modified relation of dielectric constant with higher electric field is derived by considering the Gibbs free energy modified with an external electric field and a spontaneous polarization. The result from the modified equation is in agreement with the experimental result. A concept of degree of tunability is proposed to express quantitatively the relationship between dielectric tunahility and concentration of dopants.