Preparation and structure of the Ba-stabilised T* type cuprate LaBa0.2Gd0.8CuO4 and its fluorinated phase

A single phase material with nominal composition LaBa0.2Gd0.8CuO4 was prepa red. Rietveld refinement of X-ray powder diffraction data has confirmed tha t it adopts the T* type structure with space group P4/nmm, a = 3.86601(3) A ngstrom and c = 12.6497(1) Angstrom. By heating the mixture of as-synthesiz ed LaBa0.2Gd0.8CuO4 powder and CuF2 at 400 degrees C, a fluorinated phase h as been obtained. Although the fluorinated phase retains the same tetragona l structure, it has an enlarged unit cell of a = 3.92096(6) Angstrom and c = 12.6841(1) Angstrom. The fluorine atoms were found to occupy some of the interstitial sites in the rock salt layers, but some substitution for oxyge n at the apical oxygen sites also occurs leaving the overall carrier concen tration unchanged or even slightly reduced. Magnetic susceptibilities of bo th the original LaBa0.2Gd0.8BCuO4 and the fluorinated phase are dominated b y Gd3+ paramagnetism in the temperature range between 5 and 250 K, and no m agnetic evidence for superconductivity was found in any of the samples. (C) 2000 Elsevier Science B.V. All rights reserved.