Structure of the single-phase high-temperature superconductor YBa2Cu3O7−δ

Abstract

We have determined the crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y-Ba-Cu-O system using high-resolution neutron powder diffraction. This compound has an orthorhombic structure with space group Pmmm and lattice constants a = 3.8231 A, b = 3.8864 A, and c = 11.6807 A. The structure consists of "dimpled" Cn0 2 layers in the a-b planes loosely bonded by one-dimensional fenceIike square-planar cun, chains in the b-c planes. Recently, superconductivity above 90 K was reported by Wu et at. l in a multiphase sample with a nominal composition of V!.2 B8.,,).8 0.1 2 0 4 _ b' Subsequent studies by several groups2-S identified the superconducting compound as VEa 2 Cu} Oy. Although the metal-ion stoichiometry is wen established the structure is still in question. One of the simplest ordered perovskite structures with a YBa 2 CU3 Oy stoichiometry consists of 1: l:n stacking of cubic perovskite building blocks with Cu atoms on the cube corners, Y or Ba atoms in the center of the cube, and 0 atoms on the cube edges. From powder x-ray diffraction data Cava et al. 3 pro

PHYSICAL PROPERTIES OF SINGLE-PHASE HIGH-Tc SUPERCONDUCTOR YBa2Cu3O7

“…A small amount of BaCuO 2 (<1%) as a main impurity phase as well as very weak lines, which could be assigned to unreacted BaO and Y203, were detected. The lattice parameters determined by neutron measurements are a = 3.8235(1)/~, b = 3.8858(1)A and c ---11.6762(6)A, in good agreement with previous work [5][6]. Highly ordered oxygen vacancies in a peculiar structure were confirmed.…”

Epitaxial growth and properties of YBaCuO thin films

“…The a-axis lattice constant is around 0.381 nm in the mixture of a and c-axes oriented grains and in the pure optimized [100]-orientation. This value may be compared to 0.382 nm of bulk material [22] . Similar to c, also a increases at low T 8 • A value of 0.384 nm at Ts of 650°C indicates deviations from stoichiometry in accordance with the observed disruptions of the superconducting properties.…”

“…The vibration amplitudes are averaged for contributions ofthe atoms in the string using values of0.083 A for Ba, 0.076 A for Y, an averaged value of 0.067 A for Cu(l) and Cu (2) and an averaged value of 0.088 A for the oxygen atoms on various positions. These values are taken from high resolution neutron diffraction measurements [22]. From Fig.…”

Strain Relief Twinning Due to Vacancy Ordering in YBa2Cu3Ox

“…This leads to an orthorhombic structure of Pmmra space group with parameters a o -0. 3823 nm, b 0= 0.3886 nm, c 0= 1.1681 nm [27], actually shown in Fig. 2.…”