INVESTIGATION OF THE DEPENDENCE OF ORTHOROMBIC FACTORS ON EFFECTIVE IONIC RADIUS IN THE Ln3Ba5Cu8Ox SYSTEM (WHERE Ln– Y, Nd, Sm, Eu, Gd)

Abstract

Four superconducting compounds are widely known in the Y-Ba-Cu-O system, namely: YBa2Cu3O7-δ (Y-123), YBa2Cu4O8-δ (Y-124), Y2Ba4Cu7O14+δ (Y-247) and Y3Ba5Cu8O18+δ (Y-358). They are characterized by a layered perovskite-like structure with different numbers of CuO2 planes and CuO chains [1, 2]. It has been experimentally confirmed that as the number of CuO2 planes for HTSCscuprate superconductors increases, the superconducting transition temperature increases [3, 4]. Thus, the various characteristics of superconducting materials, and especially the electrophysical and magnetic properties, are significantly influenced by their crystal structure, the parameters of the elementary lattice, the factor of orthorhombicity and the oxygen index. This work is devoted to the establishment of the parameters of elementary cells in the system: Ln3Ba5Cu8Ox (where Ln-Y, Nd, Sm, Eu, Gd), the calculation of the factor of orthorhombicity of the obtained phases and the establishment of dependences between these values. The samples were synthesized by the classical solid-phase method. The oxides of the corresponding metals (Y, Nd, Sm, Eu, Gd, Cu) and barium carbonate in the appropriate molar ratios were ground in an agate mortar to form a homogeneous mass. The resulting mixture was calcined in the temperature range 600-950°C in increments of 50°C for 40 hours, with intermediate grinding. The polycrystalline powder was then compressed into tablets at a pressure of 100 MPa and kept for about 10 hours at 900°C in air. The phase composition was investigated by X-ray powder diffraction on a Shimadzu LabX XRD-6000 diffractometer (CuKαradiation, λ = 1.54178 Ǻ, range of angles: 5≤2θ≤90°), at room temperature. The International Powder Diffraction Standards Database (JCPDS PDF-2) was used to identify the phases. The index of X-ray diffraction pattern, determination of a wide group of crystallographic parameters was performed using an additional program INDEX and X-Ray. The coefficient of orthorhombicity for the samples was performed according to the formula [5]: = (−) (+)