New Copper Phosphates as Ionic or Mixed Conductors

Abstract

AbstractAs part of a search for solid‐state copper ion conductors, new copper phosphate compounds of the Nasicon or alluaudite type structure were synthesized. Compounds with the former structure are reported here in more depth. CuTiZrP3O12 and the previously prepared compound CuTi2P3O12 were found to be copper ion conductors with a relatively low electronic contribution, and comparable both in structure and in conductivity behaviour to both CuZr2P3O12 and the NaZr2P3O12 end‐member of the classical Nasicon composition range. In contrast to the Cu(I) halide conductors these phases are stable under ambient conditions. Partial substitution of Zr by Sc, or Ti by Cr (rather than Si for P) results in a new Cu‐rich compound Cu2ZrScP3O12, together with the previously prepared compound Cu2TiCrP3O12, both showing expectedly very high Cu+ conductivity comparable to Nasicon compounds with a similar charge carrier concentration. A new related phase CuTiCrP3O12 was also synthesized. Magnetic measurements, Wagner‐Hebb polarization and e.m.f. measurements performed to elucidate partial conductivity contributions and valence states are discussed. The e.m.f. results obtained with Cu‐activity cells reveal a predominant ionic conductance together with a minor but not negligible electronic contribution resulting in a fast copper diffusion. Cu–Fe and Cu–Mg phosphates were also prepared for the first time as first examples of quaternary compounds in the Cu–Fe–P–O and Cu–Mg–P–O system respectively. These materials, Cu1,3Fe3P3O12 and Cu2Mg3P3O12 were found to be of the alluaudite structure type, with predominant electronic conductivity at high temperature.