• Cussen, Edmund
• Rogers, J.
• Lynham, D. R.

Abstract

The compounds Ba2LnMoO6 (Ln ) Nd, Sm, Eu, Gd, Dy, Y, Er, and Yb) have been synthesized by solid-state techniques under reducing conditions at temperatures up to 1300 °C. Rietveld analyses of X-ray and neutron powder diffraction data show that these compounds adopt cation-ordered perovskite<br/>phases. At room temperature Ba2NdMoO6 and Ba2SmMoO6 adopt tetragonally distorted structures in the space groups I4/m and I4/mmm, respectively, while the data collected from all other compounds could be fitted in the cubic space group Fm3hm. Bond valence sums show that the observed tetragonal distortions<br/>are driven by the bonding requirements of Ba2+. Neutron powder diffraction data collected below TN ) 15(1) K show that Ba2NdMoO6 is triclinically distorted (I1h: a ) 5.9790(2) Å, b ) 5.9840(2) Å, c ) 8.6024(2) Å, R ) 89.854(2)°, â ) 90.056(5)°, ç ) 90.003(5)°) and that Nd3+ and Mo5+ are antiferromagnetically ordered. Magnetic susceptibility data show that this compound behaves as a Curie-<br/>Weiss paramagnet above this temperature, and no other compounds in the series show evidence of magnetic order down to 2 K. Ba2YMoO6 and Ba2YbMoO6 both remain entirely paramagnetic to 2 K due to perfect geometric frustration of the cubic lattice, indicating that next-nearest-neighbor interactions between like cations dominate over nearest-neighbor Mo-O-Ln exchange. The magnetic structure of Ba2NdMoO6 is rationalized with reference to the splitting of the t2g manifold of Mo5+ by the Jahn-Teller distortion and<br/>the associated introduction of anisotropic magnetic superexchange.

Topics

• perovskite
• impedance spectroscopy
• compound
• phase
• anisotropic
• susceptibility
• space group