Ag3Ni2O4—A new stage-2 intercalation compound of 2H-AgNiO2 and physical properties of 2H-AgNiO2 above ambient temperature

Ag₃Ni₂O₄ was obtained as single crystals from a mixture of 2H-AgNiO₂ and Ag₂O in oxygen high-pressure autoclaves (P6₃/mmc (no. 194), a=2.9331(6), c=28.313(9) Å, Z=2). It may be regarded as a stage-2 intercalation compound of the host 2H-AgNiO₂ and is the first staging compound constituted of alternating subvalent and Ag⁺ sheets, inserted between NiO₂⁻ slabs. From a structural point of view, Ag₃Ni₂O₄ represents an intermediate between AgNiO₂ and the recently reported Ag₂NiO₂. The electronic structures of 2H-AgNiO₂ and Ag₃Ni₂O₄ have been investigated based on DFT band structure calculations. The high-temperature characteristics of the starting material 2H-AgNiO₂ were investigated. The inverse magnetic susceptibility, electrical resistivity and differential scanning calorimetry (DSC) show a phase transition in the temperature range of .