The dielectric permittivity was measured in the mixed crystals, as well as in the end-members. The results revealed the presence of 2 components: a dielectric response which was associated with the ferroelectric or antiferroelectric behavior, and a protonic conductivity response. Both normal and anomalous features were observed in the protonic conductivity. The normal c-axis conductivity for (Cs,NH4)H2PO4 was characterized by activation energies which ranged from 0.56eV for CsH2PO4, to 0.32eV for (Cs,NH4)H2PO4 with 40mol%NH4 in the growth solution (about 0.06mol% in the crystal). The addition of ammonium therefore increased the conductivity, but decreased the activation energy. Replacement of H with D had little effect; at least with regard to c-axis conductivity. The conductivity was anisotropic, and was considerably higher along the ferro-electric b-axis than along the a- or c-axes. The most marked anomaly was a large 20K-wide conductivity maximum, between 210 and 270K, in both (Cs,NH4)H2PO4 and (K,NH4)H2PO4. The anomalies were largely removed by applying a direct-current bias. The (K,NH4)H2PO4 data did not extend far enough above the anomalies to decide whether normal protonic conductivity occurred there.

Anomalous and Normal Protonic Conductivity in (Cs,NH4)H2PO4, (Cs,ND4)D2PO4 and (K,NH4)H2PO4. V.H.Schmidt, S.Lanceros-Mendez, S.C.Meschia, N.J.Pinto: Solid State Ionics, 1999, 125[1-4], 147-57