Unusual Phase Transformation Behaviour of Amorphous Zirconia

Pradhan, Dimple (2009) Unusual Phase Transformation Behaviour of Amorphous Zirconia. BTech thesis.



As-prepared amorphous zirconia $(ZrO_2)$ powders synthesized through different solution route were crystallized with increase in calcination temperature. Generally, the phase transformation from amorphous nature to crystalline forms of $ZrO_2$ was at around 450 °C, which was confirmed from the thermal analysis. After this phase transformation, tetragonal $ZrO_2$ slowly convert to monoclinic phase of $ZrO_2$ at higher temperature. The crystallization temperature of amorphous to tetragonal was affected by processing parameters like pH and temperature and reacting agents. The aim of the work is to shift the phase transformation behavior of tetragonal zirconia to high temperature so that zirconia should retain amorphous upto that temperature. The present work deals with a novel synthesis route for synthesizing amorphous zirconia $a-ZrO_2$ upto700 °C. In this work, $a-ZrO_2$ and nanocrystalline tetragonal zirconia $(t-ZrO2)$ were synthesized through both reduction route using sodium borohydride (NaBH4) and hydrolysis route using ammonium hydroxide (NH4OH). The synthesis has been carried out by maintaining at a constant pH (≈11). An unusual phase transformation behavior of $a-ZrO_2$ into a nanocrystalline $(t-ZrO2)$ was observed at above 900 °C in case of reduction route. Amorphous ZrO2 was used for high k-gate dielectric application due to its thermodynamically stable in contact with Si-single layer structure and its excellent reliability. Here, in this work, $a-ZrO_2$ has been successfully synthesized and that remains amorphous upto 700 °C. Above 700 °C, $a-ZrO_2$ slowly transformed into $(t-ZrO2)$and that remains stabilized upto 900 °C. Thermal, structural, microstructural and IR characterization have been studied for analyzing the $a-ZrO_2$ as well as crystalline $(t-ZrO2)$. Technologically, if one can make amorphous ZrO2 thin film which remains amorphous upto at least 800 °C could be a very useful material for electronic industries.

Item Type:Thesis (BTech)
Uncontrolled Keywords:Zirconia,Amorphous,Sodium borohydride
Subjects:Engineering and Technology > Ceramic Engnieering > Zirconia
Divisions: Engineering and Technology > Department of Ceramic Engineering
ID Code:986
Deposited By:Dimple Pradhan
Deposited On:14 May 2009 11:37
Last Modified:17 May 2009 13:06
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Supervisor(s):Nayak, B B

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