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); Angst rom and refined to the reliability factors of R(F) = 0.0366 and wR (F2 ) = 0.0782 for 102 variables and 5352 reflections. A structural featur e of interest is the presence of zigzag chains of tr trans-corner-shar ing octahedra of composition MoO55- parallel to the b-axis. Resistivit y data taken along the b-axis direction show semiconducting behavior i n the range 140 to 298 K with an activation energy of 0.16 eV. The mag netic susceptibility is quite complex. The main feature is a broad max imum at 655 K which is interpreted as due to intrachain spin correlati ons of the Mo(5 +) ions. Assuming the S = 1/2 Heisenberg model this im plies 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 str uctural 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.