### authors

- MUĂ‘OZ CASTELLANOS, ANGEL
- ALONSO, J.A
- MARTINEZ-LOPE, M.J.
- FERNANDEZ-DIAZ, M.T.

- JOURNAL OF SOLID STATE CHEMISTRY Journal

- July 2009

- 1982

- 1989

- 7

- 182

- 0022-4596

- The crystallographic structure of DyNiO3 has been investigated at T=200, 100, and 2 K from high-resolution neutron powder diffraction (NPD) data. We show that the structure is monoclinic, space group P21/n, from the metal&-insulator transition temperature at TMI=564 K down to 2 K. The Ni atoms occupy two different sites 2d (Ni1) and 2c (Ni2), whose valences, estimated from bond-valence consideration, are +2.43(1) and +3.44(1) at 2 K, respectively. This is interpreted as the result of a partial charge disproportionation of the type 2Ni3+→Ni1(3−delta)++Ni2(3+delta)+, with delta≈0.55 at T=2 K. The magnetic structure has been studied from a NPD pattern at T=2 K, well below the establishment of the antiferromagnetic (AFM) ordering at TN=154 K, as well as from sequential data collected from 16 K down to 2 K. The magnetic order is defined by the propagation vector k=(1/2,0,1/2). Two possible magnetic structures are compatible with the magnetic intensities. In the second solution both Ni sublattices participate in the magnetic order, as well as Dy since it corresponds to a total disproportionation of Ni3+ to Ni2+ and Ni4+. In the second solution both Ni sublattices participate in the magnetic order, as well as Dy. The magnetic moments for Ni1 and Ni2 atoms at T=2 K are 1.8 (2) and 0.8 (2) mu;, respectively. These values are also compatible with a partial charge disproportionation. Dy3+ ions exhibit long-range magnetic ordering below 8 K. An abrupt contraction of the unit-cell volume is observed at this temperature, due to a magnetoelastic coupling. The magnetic moment for Dy3+ at T=2 K is 7.87 (6) mu