亚硝酸钠多晶与粉末中铁电相变的研究

Research of the Ferroelectric Phase Transition in the Polycrystalline and Powder of NaNO2

对NaNO2粉末与多晶材料的复介电常数随温度的变化情况进行了讨论,并研究了其铁电相变过程.结果表明:1)高温(420K以上)低频(100Hz以下)条件下,NaNO2粉末及多晶材料复介电常数的变化主要是由离子扩散引起的.而高频(105Hz,106Hz)复介电常数实部的值在相变温度附近基本与频率无关,能够反映材料的极化和结构信息.2)在443K^450K范围内,NaNO2粉末样品的激活能U为0.70eV,NaNO2多晶的激活能U为1.58eV,NaNO2多晶的激活能要大于NaNO2粉末的激活能,这说明NaNO2粉末与多晶中离子扩散可能起源于材料的本征缺陷.3)NaNO2粉末中铁电相变在复介电常数曲线上的表现比NaNO2多晶明显;临界温度Tc以上437K至440K范围内,NaNO2多晶的复介电常数实部随温度的变化曲线偏离居里-外斯定律,说明该铁电相变过程中存在反常现象,这一现象与NaNO2单晶的结果相吻合.

In this paper, complex dielectric constant with temperature of NaNO2powder and polycrystalline are discussed, and then ferroelectric phase transition processes of which are studied, the following results are gained. 1） The complex dielectric constant changes of NaNO2powder and polycrystalline material are mainly caused by the ionic diffusion at high temperature （above 420K） and low-frequency （less than 100Hz）. The real parts of the complex dielectric constants of high-frequencies （105, 106Hz） are almost independent of frequency near the phase transition temperature; and which can reflect the polarization and structure information of NaNO2 powder and polycrystalline material. 2） In the range of 443K-450K, the activation energy U NaNO2 powder is 0.70ev, while the activation energy U of NaNO2polycrystalline is 1.58ev; the activation energy of NaNO2 polycrystalline is greater than the powder sample’s, which shows that the ionic diffusion of the powder and polycrystalline of NaNO2 may caused by the intrinsic defects. 3） The ferroelectric phase transition process in NaNO2 powder is more obvious than the one in NaNO2polycrystalline on the curves of complex dielectric constants. The curve of the real part of the complex dielectric constant of NaNO2 polycrystalline versus temperature deviates from the Curie-Weiss law in the range of 437K to 440K above the critical temperature Tc, which indicates that the ferroelectric phase transition process has the abnormal phenomenon consistent with the results of single crystal NaNO2.