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

Abstract The crystal and magnetic structures of the orthoperovskite Pr 0.8 Na 0.2 MnO 3 with non-integral mean valence (Mn 3+ /Mn 4+ ) 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 T CO =215 K, followed by an antiferromagnetic arrangement of the pseudo-CE type at T N =175 K. Under high external pressures, a microscopically separated state is formed, consisting of a mixture of the A-type AFM phase ( T N ∼155 K) and metastable FM regions ( T C ∼175 K). A possible reason for the appearance of the A-type AFM phase is the compression anisotropy which leads to marked apical contraction of MnO 6 octahedra under high pressure and creates favorable conditions for appearance of the d( x 2 − y 2 ) orbital polarization, prerequisite for the A-type AFM order. It is argued that the pressure-induced structural changes in Pr 0.8 Na 0.2 MnO 3 are accompanied by an insulator–metal transition.