Structural study of Pr0.8Na0.2MnO3 at high pressure

The crystal and magnetic structures of the orthoperovskite Pr0.8Na0.2MnO3 with non-integral mean valence (Mn3+/Mn4+) have been studied by means of powder neutron diffraction up to high-quasi-hydrostatic pressure of 4.6 GPa. At normal conditions, the system undergoes a charge ordering transition at <f>TCO=215</f> K, followed by an antiferromagnetic arrangement of the pseudo-CE type at <f>TN=175</f> K. Under high external pressures, a microscopically separated state is formed, consisting of a mixture of the A-type AFM phase (<f>TN∼155</f> K) and metastable FM regions (<f>TC∼175</f> K). A possible reason for the appearance of the A-type AFM phase is the compression anisotropy which leads to marked apical contraction of MnO6 octahedra under high pressure and creates favorable conditions for appearance of the <f>d(x2−y2)</f> orbital polarization, prerequisite for the A-type AFM order. It is argued that the pressure-induced structural changes in Pr0.8Na0.2MnO3 are accompanied by an insulator–metal transition. [Copyright &y& Elsevier]