ABSTRACT

The heat capacity and magnetisation of the obtained by the solid-phase method from simple oxides single-phase compound Ba₂FeMoO_6-δ, in which the superstructural ordering of Fe and Mo cations occurs, was studied. The anomalous behaviour of the temperature dependences of heat capacity (deviation from Debye T³ law) and magnetic moment (ZFC mode) is interpreted as the existence of a superparamagnetic state in nanoscale grains. The second λ-type anomaly of heat capacity in the region of 300 K is due to the transition of the compound from the ferrimagnetic to the paramagnetic state. The Curie temperature, determined from the maximum of excess heat capacity in the region, is in good agreement with the Curie temperature obtained from the results of magnetic measurements, T_C = 302 K. Based on the Ba₂FeMoO_6-δ compounds heat capacity data the next thermodynamic functions were calculated: reduced enthalpy, entropy, reduced Gibbs energy. The values of calculated functions in the region of temperature anomalies made it possible to classify such anomalies as second-order phase transitions.

摘要

研究了通过固相法从简单氧化物单相化合物 Ba ₂ FeMoO _6-δ获得的热容和磁化强度，其中 Fe 和 Mo 阳离子发生超结构有序。热容量的温度依赖性的异常行为（与 Debye T ^{3 的}偏差）定律）和磁矩（ZFC 模式）被解释为纳米级晶粒中超顺磁态的存在。300 K 区域内的第二个 λ 型热容异常是由于化合物从亚铁磁性状态转变为顺磁性状态。居里温度由该区域的最大过剩热容量确定，与从磁测量结果获得的居里温度非常一致，T _C  = 302 K。基于 Ba ₂ FeMoO _6-δ化合物热容数据 计算下一个热力学函数：折减焓、熵、折减吉布斯能。温度异常区域中计算函数的值使得将此类异常分类为二阶相变成为可能。