Crystal structure and phase stability of the new metallic lanthanum strontium copper oxide

Abstract The structure of (La 1−x Sr x ) 4 Cu 4 O 10 (x=0.1429) has been reexamined by neutron powder diffraction techniques. The results confirm the structural model based on the X-ray powder diffraction data. The general structural features of this material are similar to those of the other three-dimensional oxygen-deficient perovskites BaLa 4 Cu 5 O 14− δ , (La 1−x Sr x ) 8 Cu 8 O 20− δ (0.16≤x≤0.24) and La 2 Sr 6 Cu 8 O 18− δ ; in particular the oxygen vacancies in the basal plane are ordered along [001]. The framework of [Cu 4 O 10 ] consists of one type of corner-shared CuO 5 groups. X-ray powder diffraction and thermal analysis investigations showed that the orthorhombic phase (La 1−x Sr x ) 4 Cu 4 O 10 (x=0.1429) is thermodynamically stable at low temperature ( 1−x Sr x ) 4 Cu 4 O 10 to tetragonal (La 1−x Sr x ) 8 Cu 8 O 20 (x=0.1429) above 500°C is slow and occurs over a wide temperature range, characteristic of a second-order transition.