Abstract
A new compound LaSrCu0.4Al0.6O4−δ has been prepared by sol gel method, annealed at 1623 K in oxygen gas flow and examined by X-ray diffraction. Rietveld refinement shows that the sample adopts the K2NiF4-type structure, space group I4/mmm (a = 3.7694(2) and c = 12.8248(5) Ǻ, Z = 2). Vibrational properties were investigated using Raman scattering and the most characteristic vibrations are discussed with reference to the available structural data. Differential thermal analysis shows two endothermic effects at 329 and 593 K and one exothermic at 693 K. Dielectric study as a function of temperature in the frequency range of 1 kHz–1 MHz has confirmed the observed phase transitions. The value of the measured dielectric constant depends on the frequency and undergoes a large increase near the phase transition temperatures indicating a diffuse behavior of these transitions. Variation of conductivity as a function of temperature shows that the compound has a semiconducting behavior. Oxygen vacancies could be the possible ionic charge carriers. The electrical transport mechanism agrees with Adiabatic Small Polaron Hopping model.
Highlights
Ruddlesden–Popper (RP) phases with the general formula An?1BO3n?1 (A = alkali earth, rare earth elements, B = transition metal cations) are built of n(ABO3) perovskite blocks separated by a single rock salt layer (AO), and are ideal candidates for layer-by-layer assembly
The electrical transport mechanism agrees with Adiabatic Small Polaron Hopping model
A monophasic Rietveld refinement was applied for the LaSrAl0.6Cu0.4O4-d sample by FULLPROF program, using reflections associated to tetragonal cell
Summary
Ruddlesden–Popper (RP) phases with the general formula An?1BO3n?1 (A = alkali earth, rare earth elements, B = transition metal cations) are built of n(ABO3) perovskite blocks separated by a single rock salt layer (AO), and are ideal candidates for layer-by-layer assembly. They have attracted a lot of attention in various areas of materials science. Oxygen defect K2NiF4-type oxides La2-xSrxCuO4?-d are produced by heterovalent substitution of lanthanum by strontium for a wide composition range: 0 B x(Sr) B 1.34. Three domains have been characterized: orthorhombic compounds for 0 B x(Sr) B 0.1, tetragonal oxides for 0.10 B x \ 1 and several superstructures (ref oxygen defect) for 1 B x(Sr) B 1.34. The oxygen nonstoichiometry of the tetragonal form of La2-xSrxCuO4-d is due to an elimination of oxygen, while extra
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