Crystal structure and structural phase transitions in the GdBaCo2O5.0cobaltite

Abstract

We present an accurate investigation of the prototypical rare-earth cobaltite GdBaCo${}_{2}$O${}_{5.0}$ by complementary synchrotron powder and conventional source single-crystal x-ray diffraction experiments. The correct space group (Pmmm) and the accurate crystallographic structure of this compound at room temperature (RT) have been determined. By increasing $T$ a second-order structural-phase transition to a tetragonal structure with space group $P$4/mmm at $T$ \ensuremath{\approx} 331 K is found. Close to the N\'eel temperature (${T}_{\mathrm{N}}$ \ensuremath{\approx} 350 K), anomalies appear in the trend of the lattice constants, suggesting that the structural phase transition is incipient at ${T}_{\mathrm{N}}$. A possible mechanism for this complex behavior is suggested.