Curie Temperature Kit

Objective: Determination of dielectric constant of PZT material with Temperature variation and thus determining Curie Temperature.

Theory: Ferro-electricity usually disappears above a certain temperature called the transition (or Curie) temperature. Knowledge of the Curie temperature and the variation of the dielectric constant below and above the Curie temperature are of interest to the physicists and the engineers.

In this experiment an LC circuit is used to determine the capacitance of the dielectric cell and hence the dielectric constant. The circuit details are shown below:

DC : Dielectric Cell

SC : Standard Capacitor

L : Induction

X : Ferroelectric Sample

The dielectric cell DC is placed in PID controlled hot air furnace. The temperature of the furnace can be measured by inserting a thermocouple in a hole (provided on one of the Teflon discs), so that it touches one of the capacitor (metal) plates.

The audio oscillator is incorporated inside the instrument. If CSC and CDC represent the capacitances of the standard capacitor and dielectric cell respectively and if VC1 and VC are the voltages across SC and DC then

By measuring VSC & VDC and using the value of CSC we can determine the capacitance of the dielectric cell containing the sample.

If C0 represents the capacitance of the dielectric cell without the crystal and the plates separated by air gap whose thickness is the same as the thickness of the crystal then C0 is given by

Where r represents the radius of the crystal and d represents its thickness

The dielectric constant of the crystal at any given temp. is given by

The Setup facilitates determination of dielectric constant of PZT sample at different temperature. Dielectric Constant increases as temperature increases, and near Curie temperature, it shows a steep increase and reaches a peak at Curie Temperature.