Nanoscale Structural Features of Ultra-fine Zirconia Powders Obtained Via Precipitation-hydrothermal Treatment Route
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Nanoscale structural features of ultra-fine zirconia powders obtained via precipitationhydrothermal treatment route Vladislav A. Sadykov1,2, Vladimir I. Zaikovskii1, Dmitrii A. Zyuzin1, Ella1 M. Moroz, Elena1 B. Burgina, Arcady V. Ishchenko2, Vitaly G. Kostrovskii3, Valerii A. Matyshak4 1
Boreskov Institute of Catalysis SB RAS, pr. Lavrentieva, 5, 630090, Novosibirsk, Russia; Novosibirsk State University, Novosibirsk, Russia; 3 Institute of Solid State Chemistry SB RAS, Novosibirsk, Russia. 4 Semenov Institute of Chemical Physics RAS, Moscow, Russia. 2
ABSTRACT Genesis of the structure of zirconia fine particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO3)2 solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 oC has been studied by HRTEM, X-ray diffraction, Raman and FTIRS. HTT rearranges the structure of amorphous zirconia, which helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) after a mild calcination at 500 oC. Dehydroxilation and sintering of these nanoparticles at higher (600-650 oC) temperatures generate polysynthetic (001) twins. Modeling revealed that reappearance of the (111) “cubic” reflex in XRD patterns of samples calcined at 600-650 oC can be due to these extended defects. In their vicinity, the seven-fold Zr-O coordination sphere is retained, while packing of ZrO7 polyhedra is varied towards more symmetric structures, thus causing disappearance of the Raman spectra. INTRODUCTION Zirconia is among the most refractory, shock-resistant and corrosion-resistant oxides, which determines its broad industrial application including construction ceramics, corrosionresistant and thermal –barrier coatings, gas sensors, solid electrolytes, catalysts etc [1]. It is now well recognized that using the nanocrystalline zirconia allows to improve functional properties of these materials. Hydrothermal treatment (HTT) of amorphous precipitated zirconium hydroxide facilitates its crystallization at moderate temperatures [2] thus ensuring nanocrystallinity. Usually, XRD is used to study dependence of zirconia phase composition and structural features on the nature of starting salts, precipitation and HTT conditions. As a result, fine details of zirconia nanostructure determining the relative stability of zirconia polymorphs are still the subject of discussion [3-5]. So the aim of this paper was to apply combination of diffraction (XRD, TEM) and spectroscopic (Raman, FTIRS) methods to study specificity of the phase composition and structural details of nanocrystalline zirconia particles prepared via HTT of amorphous hydrous zirconia followed by subsequent progressive annealing under air. These data are required to elucidate atomic-scale factors determining performance of nanocrystalline ZrO2 samples as efficient catalysts of the reaction of NOx selective reduction by propylene in the excess of oxygen [6, 7]. EXPERIMENTAL Samples of zirconia were prepared by a method similar to
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