Effect of crystallization water on the structural and electrical properties of CuWO_4 under high pressure

摘要

The effect of crystallization water on the structural and electrical properties of CuWO_4 under high pressure has been investigated by in situ X-ray diffraction and alternating current impedance spectra measurements. The crystallization water was found to be a key role in modulating the structural stability of CuWO_4 at high pressures. The anhydrous CuWO_4 undergoes two pressure-induced structural transitions at 8.8 and 18.5 GPa, respectively, while CuWO_4·2H_2O keeps its original structure up to 40.5 GPa. Besides, the crystallization water makes the electrical transport behavior of anhydrous CuWO_4 and CuWO_4·2H_2O quite different. The charge carrier transportation is always isotropic in CuWO_4·2H_2O, but anisotropic in the triclinic and the third phase of anhydrous CuWO_4. The grain resistance of CuWO_4·2H_2O is always larger than that of anhydrous CuWO_4 in the entire pressure range. By analyzing the relaxation response, we found that the large number of hydrogen bonds can soften the grain characteristic frequency of CuWO_4·2H_2O over CuWO_4 by one order of magnitude.