Mahata, Bidesh and Ramadurai, Ranjit
(2019)
Structural and dielectric studies of ferroelectric Nd2Ti2O7
for high temperature pyro sensor application.
Masters thesis, Indian institute of technology Hyderabad.
Abstract
High temperature pyroelectric sensing technology is important in materials processing as well as in automotive and aerospace engineering. In aerospace it can be used as Exhaust Gas Temperature Sensor (EGTS) for hot chamber of jet engine as EGTS measures engine’s health and other sensing application. The primary requirement from the material perspective is it must be stable in high temperature range (600 to 1000° C). Ferroelectric material with high Tc (>1000°C) can be used in temperature sensing technology due to its pyroelectric properties. Neodymium Titanate (Nd2Ti2O7) is a promising candidate for this application as it has curie temperature of ~ 1480°C. NTO is a member of layered perovskite ferroelectric material. High Tc of NTO is due to the presence of dominant 180° ferroelectric domains and ferroelectric to paraelectric phase transition contains displacement of the whole sub lattice of TiO6 octahedron. In this thesis, we report the studies on synthesis of material, FullProf refinement and high temperature dielectric and pyroelectric properties of Neodymium Titanate material. Synthesis of NTO material is done by solid state reaction method. Neodymium oxide and titanium oxide is taken as primary materials in 1:2 molar ratios and the mixture is grinded with mortar and pestle for 4 hours. Phase purity is obtained by calcination of powder sample at 1250°C for 4 hours. XRD studies confirm the phase purity of neodymium titanate material. After ball milling powder is pressed to make pellet. Green pellets were sintered at 1400°C for 5 hours with a heating and cooling rates of 5°C/min. Detailed study of structural refinement was carried out by FullProf Suite software with CIF file taken from COD data base. SEM images of pellet shows densely packing of particles. Finally, dielectric property study is done by impedance analyzer instrument and furnace that goes up to 800°C. First experiment is done with applied voltage 0.8 V and data is taken during cooling from 750°C-50°C which shows the variation of dielectric constant and dielectric loss with temperature and frequency. Good curve is obtained with increasing temperature for higher frequency like 100kHz or 1kHz. For higher frequency almost no variation of dielectric viii constant and dielectric constant with temperature and that is expected as temperature range is low. Low dielectric loss for higher frequencies will be good for application. For temperature sensing application it is very important to show pyroelectricity. NTO is a ferroelectric material, so it’s must have pyroelectric property. To know its temperature sensitivity pyrocurrent measurement is done. Pellets connected with platinum wires using silver paste kept inside the furnace and wires connected to source meter unit (Keithley-2401). Current vs time data is taken with temperature ramping between 600°C to 500°C which shows exponentially increasing or decreasing current w.r.t to temperature ramping. This is called pyrocurrent. This is the evidence of pyroelectricity in NTO material for temperature sensing application.
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