Oxide electronics

Abstract:

We report the observation, in Pr0.6Sr0.4MnO3, of a low-temperature phase transition between Pnma and the monoclinic space group I2/a. The I2/a allotype has never previously been observed in the (R1-xAx)MnO3 manganese perovskite system. Furthermore, this space group symmetry is not present in the recently published phase diagram obtained at 30% Mn+4, indicating that electronic doping has a direct effect on the phase stability. The structural and magnetic parameters for the new phase, as obtained from Rietveld refinements of neutron powder diffraction data, are also reported. © 1996 Academic Press.

Abstract:

The structural phase diagram of A 1-x A′ x MnO 3 (A = La, Pr, Y, ...; A′ = Ca, Sr, Ba, ...) as a function of the average A-site ionic radius 〈r A 〉 was determined from neutron powder diffraction data. In addition to the well-known Pnma and R3̄c phases, a new orthorhombic phase, with space group Imma, was found for large 〈r A 〉 at low temperatures. Refined structural parameters are reported for La 0.7 Ba 0.3 MnO 3 at 1.6 K (Imma) and at 293 K (R3̄c). The Imma → R3̄c phase transition was studied as a function of temperature for the same La 0.7 Ba 0.3 MnO 3 sample, and determined to be first order. © 1996 Academic Press, Inc.