Molten salt synthesis of nano structured pyrochlore lanthanum zirconate: a potential material for high temperature applications

Molten salt synthesis of nanocrystalline pyrochlore lanthanum zirconate (La₂Zr₂O₇) powders with NaCl–KCl alone as reaction aid was prepared in the present investigation with low synthesis temperature for the first time. The structural and morphological data of the synthesized lanthanum zirconate powder was characterized using XRD, FESEM—EDS and TEM. Functional group identification was carried out using FT-Ir and simultaneous themal analysis on the starting material was also carried out characterized by thermogravimetric analysis and differential thermal analysis. Simultaneous thermal analysis of the starting materials was carried out and the results show the suitability of the molten salt synthesis below 900 °C. The XRD pattern reveal the existence of pyrochlore structure La₂Zr₂O₇ matches with the standard ICDD pattern. The average crystallite size was measured to be 34.66 nm by Debye Scherer formula and 35.53 nm using WH plot. The particle size measured using the particle size analyser, scanning electron microscope and transmission electron microscope shows in the order of 40–50 nm and the powders are seen clearly without agglomerations. Energy dispersive spectrum results show the clear presence of La–Zr–O without any other inclusions and confirms the results obtained through x-ray photo emission spectroscopy. SAED pattern obtained through TEM shows the polycrystalline nature of the synthesised nano La₂Zr₂O₇. The structural functional group evolution was examined using FT-Ir confirms the formation of La–Zr–O chemical bonds. The results confirms that nano crystalline pyrocholore La₂Zr₂O₇ can be successfully synthesised using relatively low temperature molten salt route at 850 °C with the aid of anhydrous NaCl–KCl eutectic salt mixture alone as reaction aid and anhydrous La₂O₃ and ZrO₂ as precursors. (paper)