多铁性Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$体系（$0 \le x \le 0.65, 0 \le y \le 0.1$）相变的比热研究
Specific heat studies of the phase transitions in multiferroic Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$ system ($0 \le x \le 0.65, 0 \le y \le 0.1$)
AI总结：
本研究通过两种比热测试方法探究多铁性Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$体系的相变，发现含Ti样品的磁相变由连续转变为一级，且高温铁电相变异常因两相共存温区宽而难观测。
摘要：
本文报道了采用弛豫法和DSC（差示扫描量热法）在2-450 K温度范围内对Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$多晶样品开展的比热研究。研究测量并分析了伴随反铁磁-顺磁相变与铁电-顺电相变出现的比热异常。所研究的体系是一种颇具潜力的第二类多铁材料，其磁系统与电系统之间的强耦合可归因于同一种Mn$^{4+}$离子同时主导两种有序态。研究借助考虑了自由能中高阶项的先进连续相变理论，对磁相变处的比热异常进行了分析，并估算了体系临界行为的相关参数。结果发现，与此前的预测不同，含Ti样品的该相变不再具有连续相变特征，可能转变为一级相变过程。研究还发现，伴随一级高温铁电相变的比热异常在两种测试技术下都难以观测，这被归因于介电相和铁电相共存的温度范围较宽。
英文摘要：
Specific heat studies of the Sr$_{1-x}$Ba$_x$Mn$_{1-y}$Ti$_y$O$_3$ polycrystalline samples performed by the relaxation and DSC methods over the temperature range 2 - 450 K are reported. Anomalies accompanying the antiferromagnetic-paramagnetic and ferroelectric-paraelectric phase transitions were measured and analyzed. The system studied is a promising multiferroic material of the 2$^{\text {nd}}$ type, in which a strong coupling between the magnetic and electric systems can be related to the fact that the same Mn$^{4+}$ ions are responsible for the two orderings. Analysis of the anomaly at the magnetic transition was done by using the advanced theory of the continuous transitions, in which the presence of higher order terms in the free energy is considered, and the parameters of the critical behavior of the system were estimated. It was found that, despite of earlier predictions, the transition loses the continuous character and can become the 1$^{\text {st}}$ order process for the Ti-containing samples. The anomalies accompanying the 1$^{\text{st}}$ order high-temperature ferroelectric transition were found to be hardly visible by using both techniques, which was ascribed to a wide temperature range of coexistence of the dielectric and ferroelectric phases.
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