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Evidence of Phase Transition in ZrO2–CuO nanoparticles revealed by HRTEM and SAED

In this article we report on HRTEM and SAED examination of samples ZrO2–CuO having 0 and 0.2 mol % CuO content and calcinated at temperatures 400 and 5000C (samples named ZCuO-400, ZCuO2-400, ZCuO-500, ZCuO2-500). Measurements were performed on JEOL JEM 2010 200kV high resolution transmission electron microscope. Previously the samples were examined by low frequency Raman spectroscopy (LFRS) [1] and other characterization methods [2]. LFRS can be applied to nanoparticles having spherical microstructure and having constant that depends on the ratio of the longitudinal and transversal velocities of sound within the particles. The particle size distribution measured by LFRS and HRTEM is in very good agreement for number of materials whether the particles are amorphous, nanocrystaline, nanoscrystaline in amorphous matrix in thin films or in the form of powder [3]. In Figure 1. we give evidence about the existence amorphous nanoparticles, what is evidenced in BF as well in SAED, were the first amorphous ring is very well observed. By prolonged heating in SAED, monoclinic and tetragonal ZrO2 can be observed (sample ZCu0). The samples ZCuO-400 and ZCuO2-500 are fully amorphous (Figures 1b. and 2d), but with heating in EM during observation by SEAD, the first spot of new phase appeared in amorphous part of sample. The monoclinic ZrO2 (-111) with d =0.314 nm and (111) with d=0.284 nm are identified. In Figure 1c. in the same region of the sample amorphous spherical and crystalline particles as well the holes (H) are observed in HRTEM image. For lower magnification particle size distribution, the size of particles are D=(6.70.3) nm, while hole sizes are (5.70.3) nm. The crystalline phases are identified in SAED in Figures 1b. and 2b. as amorphous and monoclinic ZrO2 . In Figure 2. (sample ZCu2) particle sizes are smaller D= (3.40.6)nm (from the HRTEM image from Figure 2a.). This result is in accordance with previous measurements, obtained on series of samples having different doping concentration of CuO, in which the grain sizes increase with increasing calcinations temperature [1]. Also, the results show that with increasing dopant concentration, nanoparticles become smaller, as observed in In2O3 doped with Sn (ITO) [4].

ZrO2–CuO nanoparticles; High Resolution Transmission Electron Microscopy (HRTEM); Selected Area Electron Diffraction (SAED)

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