Crystallochemical and magnetic studies of the mixed pyrovanadates Zn _xM_2-xV₂O₇ ( 0 ≤ x ≤ 2) ( M = Ni, Cu)

The mixed pyrovanadates Zn_xM_2-xV₂O ₇ ( 0 ≤ x ≤ 2) ( 0 ≤ x ≤ 2) ( M = Ni, Cu), were prepared by solid way starting from the reagents ZnO, NiO or CuO and (NH ₄)VO₃. The IR spectroscopy enables us to identify the V₂O₇^4-groups as well as the nature of their conformation. The stability ranges of different phases are delimited by XRD. A continuous solid solution β-(Zn,Cu) ₂V₂O₇ is observed in a wide range ( 0.2 ≤ x ≤ 2). The phase β-Cu ₂V₂O₇ is stabilised at ambient temperature by substitution of 10% of Cu²⁺ ions by the Zn²⁺ ions. The pyrovanadates ZnNiV₂O₇ and ZnCuV₂O₇ exhibit a ferrimagnetic behaviour explained by the existence of not compensated magnetic sublattices.