Spontaneous polarization in the deuterated and undeuterated proton glass Rb1-x(NH4)xH2AsO4

The authors report an investigation of the spontaneous polarization (SP) of mixed single crystals of rubidium ammonium dihydrogen arsenate (RADA) and its deuterated counterpart (DRADA) as well as of pure ferroelectric rubidium dihydrogen arsenate (RDA) and its deuterated counterpart (DRDA). There is a sharp rise in the SP at the ferroelectric transition temperature T_c for the pure crystals as this transition is first order. The change in the SP in the mixed (x=0.08) crystals below T_c is gradual, however, indicating the presence of acid hydrogen and ammonium cations that are still mobile and in the paraelectric phase. These mixed crystals show the coexistence of paraelectric/proton glass and ferroelectric order below the glass transition temperature T_g. The maximum values of SP in the deuterated samples are greater than in the undeuterated samples. The maximum values of SP in the mixed crystals below T_c at the lowest temperatures studied is found to be slightly lower than the corresponding value in the pure crystals