Abstract
High-pressure behaviours of isomorphousHoMn2O5 andBiMn2O5 (Pbam, Z = 4) were studied, using Raman spectroscopy and single-crystal x-ray diffraction,with the samples in diamond anvil cells pressurized to 10.09 GPa and 8.54 GPa,respectively, at room temperature. No phase transition was detected ineither material. The two manganates are most compressible along thea axis with the latticecontractions along the b and c directions nearlythe same. Their P–V data fitted with the second-order Birch–Murnaghan equation of state (B′ = 4.0) give thebulk moduli B0 = 138(2) GPa for BiMn2O5 and B0 = 173(3) GPa for HoMn2O5. The difference in bulk moduli results fromBiMn2O5 being morecompressible than HoMn2O5 along the a axis. Our study shows that the Mn–O frameworks in isomorphousRMn2O5 compounds(R = Bi and rare earth) are not rigid at high pressures, but rather adapt to the behaviour of thecoordination spheres around the R atoms. Bond valence calculations indicate that thepressure-induced charge transfers between the two Mn sites have different characters for thetwo compounds.
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