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A closer look at superionic phase transition in (NH4)4H2(SeO4)3: impedance spectroscopy under pressure.
Acta Crystallographica Section B ( IF 1.3 ) Pub Date : 2020-04-15 , DOI: 10.1107/s2052520620003741 Łukasz Lindner 1 , Maria Zdanowska-Frączek 1 , Zbigniew Czapla 2 , Ziemowit Frączek 1
Acta Crystallographica Section B ( IF 1.3 ) Pub Date : 2020-04-15 , DOI: 10.1107/s2052520620003741 Łukasz Lindner 1 , Maria Zdanowska-Frączek 1 , Zbigniew Czapla 2 , Ziemowit Frączek 1
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The proton‐conducting material (NH4)4H2(SeO4)3 is examined to check whether its conductivity spectra are sensitive to subtle changes in the crystal structure and proton dynamics caused by external pressure. The AC conductivity was measured using impedance spectroscopy, in the frequency range from 100 Hz to 1 MHz, at temperatures 260 K < T < 400 K and pressures 0.1 MPa < p < 500 MPa. On the basis of the impedance spectra, carefully analyzed at different thermodynamic conditions, the p–T phase diagram of the crystal is constructed. It is found to be linear in the pressure range of the experiment, with the pressure coefficient value dTs/dp = −0.023 K MPa−1. The hydrostatic pressure effect on proton conductivity is also presented and discussed. Measurements of the electrical conductivity versus time were performed at a selected temperature T = 352.3 K and at pressures 0.1 MPa < p < 360 MPa. At fixed thermodynamic conditions (p = 302 MPa, T = 352.3 K), the sluggish solid–solid transformation from low conducting to superionic phase was induced. It is established that the kinetics of this transformation can be described by the Avrami model with an effective Avrami index value of about 4, which corresponds to the classical value associated with the homogeneous nucleation and three‐dimensional growth of a new phase.
中文翻译：
仔细研究（NH4）4H2（SeO4）3中的超离子相变：压力下的阻抗谱。
检查质子传导性材料（NH 4）4 H 2（SeO 4）3，以检查其电导率光谱是否对晶体结构的细微变化以及由外部压力引起的质子动力学敏感。使用阻抗谱在100 Hz至1 MHz的频率范围内，温度260 K < T <400 K和压力0.1 MPa < p <500 MPa的条件下测量交流电导率。根据阻抗谱，在不同热力学条件下仔细分析，p – T晶体的相位图已构建。发现在实验压力范围内是线性的，压力系数值d T s / d p = -0.023 K MPa -1。还介绍并讨论了静水压力对质子传导性的影响。在选定的温度T = 352.3 K且压力为0.1 MPa < p <360 MPa的条件下进行电导率随时间的测量。在固定的热力学条件下（p = 302 MPa，T= 352.3 K），导致低速固相转变为超离子相。已经确定，该转变的动力学可以由Avrami模型描述，有效Avrami指数值约为4，该值对应于与新相的均匀成核和三维生长相关的经典值。
更新日期：2020-04-15
中文翻译：
仔细研究（NH4）4H2（SeO4）3中的超离子相变：压力下的阻抗谱。
检查质子传导性材料（NH 4）4 H 2（SeO 4）3，以检查其电导率光谱是否对晶体结构的细微变化以及由外部压力引起的质子动力学敏感。使用阻抗谱在100 Hz至1 MHz的频率范围内，温度260 K < T <400 K和压力0.1 MPa < p <500 MPa的条件下测量交流电导率。根据阻抗谱，在不同热力学条件下仔细分析，p – T晶体的相位图已构建。发现在实验压力范围内是线性的，压力系数值d T s / d p = -0.023 K MPa -1。还介绍并讨论了静水压力对质子传导性的影响。在选定的温度T = 352.3 K且压力为0.1 MPa < p <360 MPa的条件下进行电导率随时间的测量。在固定的热力学条件下（p = 302 MPa，T= 352.3 K），导致低速固相转变为超离子相。已经确定，该转变的动力学可以由Avrami模型描述，有效Avrami指数值约为4，该值对应于与新相的均匀成核和三维生长相关的经典值。
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