Publications by Paolo Radaelli


Ba<inf>2</inf>YFeO<inf>5.5</inf>: A ferromagnetic pyroelectric phase prepared by topochemical oxidation.

Chemistry of Materials 25 (2013) 1800-1808

K Luo, RD Johnson, TT Tran, PS Halasyamani, PG Radaelli, MA Hayward

Reaction of the anion-deficient, cation-ordered perovskite phase Ba 2 YFeO 5 with 80 atm of oxygen pressure at 410 C results in the formation of the Fe 4+ phase Ba 2 YFeO 5.5 . The topochemical insertion of oxide ions lifts the inversion symmetry of the centrosymmetric host phase, Ba 2 YFeO 5 (space group P2 1 /n), to yield a noncentrosymmetric (NCS) phase Ba 2 YFeO 5.5 (space group Pb2 1 m (No. 26), a = 12.1320(2) Å, b = 6.0606(1) Å, c = 8.0956(1) Å, V = 595.257(2) Å 3 ) confirmed by the observation of second-harmonic generation. Dielectric and PUND ferroelectric measurements, however, show no evidence for a switchable ferroelectric polarization, limiting the material to pyroelectric behavior. Magnetization and low-temperature neutron diffraction data indicate that Ba 2 YFeO 5.5 undergoes a magnetic transition at 20 K to adopt a state which exhibits a combination of ferromagnetic and antiferromagnetic order. The symmetry breaking from centrosymmetric to polar noncentrosymmetric, which occurs during the topochemical oxidation process is discussed on the basis of induced lattice strain and an electronic instability and represents a new strategy for the preparation of NCS materials that readily incorporate paramagnetic transition metal centers. © 2013 American Chemical Society.


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