Microstructures And Electrical Properties Of Cathode Materials Ln_0.5Sr_0.5CoO_3-δ (Ln=La, Pr, Nd,) Thin Films

Thin films of Ln_0.5Sr_0.5CoO_3-δ(Ln =La, Pr, Nd)were grown on yttria-stabilizedzirconia (YSZ) single crystal substrates, aluminate lanthanum (LaAlO₃)single crystalsubstrates and SiO₂ substrates by ion-beam sputtering method. Then theLn_0.5Sr_0.5CoO_3-δthin films were heat-treatmented at difference temperature from450℃to 750℃. The X-ray diffraction (XRD) spectra, Scanning Electron Microscopy(SEM) and X-ray photoelectron spectroscopy (XPS) were measured forLn_0.5Sr_0.5CoO_3-δthin films. The surface microstructures, chemical states were studiedfor Ln_0.5Sr_0.5CoO_3-δthin films, also, The conductivity of the specimen was measuredby four-probe method.The results of the XRD spectra show that the Ln_0.5Sr_0.5CoO_3-δthin films whichare on the YSZ and LaAlO₃ have the tendency to strengthen in orientation of<110>and <100> respectively, when the heat-treatment temperature reach 750℃, theLn_0.5Sr_0.5CoO_3-δthin films samples would become a steady and unitary Perovskitephase.The results of XPS show that the chemical states of the Ln_0.5Sr_0.5CoO_3-δthinfilms are Ln³⁺(Ln³⁺=La³⁺, Pr³⁺, Nd³⁺), Sr²⁺,Co³⁺,Co⁴⁺,O^2-.There are two kinds ofoxygen which are crystal lattice oxygen and absorbed oxygen on the films, also, Theoxygen vacancies of Ln_0.5Sr_0.5CoO_3-δthin films deposited on YSZ substrates arebigger than that deposited on LaAlO₃ substrates respectively. The oxygen vacanciesare the biggest for Nd_0.5Sr_0.5CoO_3-δ/YSZ thin film. It is of benefit to enhancing the oxygen ionic transport properties.SEM results show Ostwald growth and the dispersed island structures weredisplayed on the La_0.5Sr_0.5CoO_3-δthin films which heat-treatmented at 550℃. Whenheat-treating at 750℃, the grain size of La_0.5Sr_0.5CoO_3-δthin films become bigger andthe dispersed islands are collected; The Pr_0.5Sr_0.5CoO_3-δthin film presents along-range order structures and shows dendritic growth.The maximum of conductivity appears at about 700℃, The DC conductivityArrhenius plots are approached to linearity at low temperature, indicates theconductivity behavior of specimen is consistent with the small polaron mechanism;The AC conductivity shows the switch over from grain-boundary process at lowfrequency to the bulk conduction process at high frequency.