A study of the structure and electronic and thermal properties of quasi-one-dimensional La3MoO7

The structure of La3MoO7 was solved in P2(1)2(1)2(1) with Z = 4 and a = 7.597(1) Angstrom, b = 7.7192(4) Angstrom, and c = 11.0953(8); Angstrom and refined to the reliability factors of R(F) = 0.0366 and wR (F2) = 0.0782 for 102 variables and 5352 reflections. A structural feature of interest is the presence of zigzag chains of tr trans-corner-sharing octahedra of composition MoO55- parallel to the b-axis. Resistivity data taken along the b-axis direction show semiconducting behavior in the range 140 to 298 K with an activation energy of 0.16 eV. The magnetic susceptibility is quite complex. The main feature is a broad maximum at 655 K which is interpreted as due to intrachain spin correlations of the Mo(5 +) ions. Assuming the S = 1/2 Heisenberg model this implies a J/k= - 511 K. Several other anomalies are observed at 483, 140, and 100 K. Differential scanning calorimetry data also show the 483 K feature and disclose another at 373 K not seen in the susceptibility. There is no evidence from powder neutron diffraction data of any structural changes from 298 to 10 K but no data are available above room temperature. There is an indication from neutron diffraction data for the onset of long-range antiferromagnetic order below 100 K. (C) 1997 Academic Press.