Thermal Expansion Properties of Ag2O Crystal Structure by Powder Neutron Diffraction

Abstract

Silver Oxide (Ag2O) is known as one of components in super ionic glass of AgI-Ag2O-V2O5 which is expected practical application for a solid electrolyte of a storage battery cell. The crystal structure of Ag2O is so called cuprite structure, and it belongs to the space group Pn-3m (#224, Oh). As a viewpoint of thermal properties, it is reported that the Ag2O shows the negative thermal expansion below 200 K, and nonlinear dependency of lattice constants by Srivastava [1]. In addition, Wada investigated the residual pressure effect based on the relation between integral breadth and pressing force by Willamson-Hall plot methods from X-ray powder diffraction [2]. In order to clarify the thermal relaxation effect of Ag2O which is applied pressing force, it is necessary to discuss the temperature dependency of thermal expansion in detail. Indeed, it was reported the negative thermal expansion of Ag2O above room temperature by using X-ray powder diffraction by Tiano [3]. On the other hand, the neutron diffraction has advantages for accurate refinement of lattice parameters in term of high transmittance compared with the horizontal typed Bragg-Brentano geometry by X-ray powder diffraction. Moreover, since in the neutron diffraction the coherent scattering length is not dependent on scattering angle, it is able to determine accurate temperature factors. Powder neutron measurements were performed with ECHIDNA at ANSTO in the temperature range from 3 K to 400 K. The wavelength used 1.3 A, calibrated against NIST Si, and the effective angular range was 8-155 degree. These neutron diffraction data were refined by Z-Rietveld. Details of the discussion will be introduced at the presentation. This study was supported by Grant-in-Aid for Scientific Research (C), 24510117.