Structure and Magnetism in CrTa2O6: A Trirutile Oxide Based on Cr2+

CrTa2O6, a rare example of an oxide containing Cr2+, was prepared by solid state reaction from a mixture of Cr2O3, Ta2O5, and Ta in a sealed silica tube at 1050°C. It exhibits a slightly distorted trirutile structure described inP21/nwitha=4.738(1),b=4.7421(6),c=9.2972(9), andβ=90°55′(1) as determined from Guinier–Hagg data and CuKα1radiation, in excellent agreement with previous reports. The crystal structure was refined from powder neutron diffraction data at 20 K. The Cr2+environment is distorted from that usually found in trirutile oxides with Cr–O distances ranging from 2.06(1) to 2.270(9) Å consistent with a static Jahn–Teller distortion as expected for high-spin Cr2+. Magnetic susceptibility data show a Curie–Weiss behavior withC=2.79(1) emu mol−1K−1, which compares well with the expected value of 3.0 emu mol−1K−1for the high-spin state. Aθc=−30.0(8) K indicates the dominance of antiferromagnetic exchange. A susceptibility maximum at 11 K is evidence for long-range antiferromagnetic order. Low-temperature neutron diffraction data confirm aTN=10.3(1) K and a complex magnetic structure with ordering wave vectork̂=(1/4 1/4 1/4) as seen for some other trirutile oxides. ForT>TN, two-dimensional, short-range correlations are seen in the form of a Warren line shape. Interestingly, the two-dimensional correlations persist into the ordered regime, at least to 9.0 K. The properties of CrTa2O6are compared with other known trirutileMTa2O6andMSb2O6materials.