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Abstract: The properties of RbH2PO4/SiO2 composites with different SiO2 pore sizes, prepared by mechanical milling, have been investigated here by various methods. The protonic conductivity is found to depend significantly on SiO2 pore size: the smaller the pore size, the stronger the conductivity enhancement in low-temperature (LT) region, comparing with pure RbH2PO4. The improved conductivity in composites arises from the formation of interface phase layer due to surface interaction between two components. This layer with thickness of ~4nm is structurally disordered or amorphous RbH2PO4 phase, which exhibits the orientation-disorder of H2PO4 − anions induced by the weakening of H-bonds. The interfacial layer exists on the surfaces or inside the pores of SiO2 particles, creating a continuous proton-conductive pathway and leading to the faster proton movement and greater conductivity even at LT. [Copyright &y& Elsevier]

Abstract: The protonic conductivity of (1− x)RbH2PO4–xSiO2 composites prepared by mechanical milling has been investigated in the humid atmosphere. In comparison with pure RbH2PO4, the conductivity enhancement was observed and it was strongly dependent on the amount of SiO2 additives. At low-temperature (LT) phase, the conductivity of composites increased with the addition of SiO2 till x =0.6 at which the maximum conductivity reached. At high-temperature (HT) phase, it was approximately equal to that of pure RbH2PO4 and almost kept unchanged till x =0.5. Therefore, the jump in conductivity at ∼280°C (superprotonic phase transition temperature of RbH2PO4) tended to decrease as x increased and finally disappeared. Furthermore, the conductivity of both LT and HT phases went down at large x values. The conductivity enhancement has been confirmed not to be influenced by absorbed water on the surface of SiO2 particles. In fact, it is due to the formation of structurally disordered or amorphous interface phase. Also, we summarized the different theoretical models of the conductivity enhancement in composites. [Copyright &y& Elsevier]