Evidence for monoclinic crystal structure and negative thermal expansion below magnetic transition temperature in Pb(Fe1/2Nb1/2)O-3

Abstract

The existing controversy about the room temperature structure of multiferroic Pb(Fe1/2Nb1/2)O-3 is settled using synchrotron powder x-ray diffraction data. Results of Rietveld refinements in the temperature range of 300-12 K reveal that the structure remains monoclinic in the Cm space group down to 12 K, but the lattice parameters show anomalies at the magnetic transition temperature (T-N) due to spin-lattice coupling. The lattice volume exhibits negative thermal expansion behavior, with alpha=-4.64x10(-6)K(-1), below T-N. (c) 2007 American Institute of Physics.