Dear friend Sudhansu Sekhar Hota

The dielectric and impedance properties of ceramic material change with temperature. When you cool the furnace from high temperature to low temperature, the properties of ceramic material will change accordingly (Investigation of the dielectric....). The impedance and AC conductivity measurement confirm the NTCR behavior of the synthesized nanocomposites, and the Cole-Cole plots revealed the nanocomposite's bulk resistance behavior by the appearance of well-defined semicircular arcs at the higher frequencies (Investigation of the dielectric....). It was found that three dielectric responses were observed in complex impedance plots and HTDR was involved with the movement of oxygen vacancies (High‐temperature dielectric properties....). Activation energy calculated from dielectric data suggested that the HTDR was governed by the hopping conduction process High‐temperature dielectric properties...).

I hope this helps! Let me know if you have any other questions.

Source:

(1) Investigation of the dielectric and impedance ... - ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0921452620303653.

(2) High‐temperature dielectric properties and impedance spectroscopy of .... https://ietresearch.onlinelibrary.wiley.com/doi/10.1049/iet-nde.2020.0030.

(3) Dielectric spectroscopy - Wikipedia. https://en.wikipedia.org/wiki/Dielectric_spectroscopy.

When studying the dielectric, electrical, and impedance properties of ceramic materials, it is important to consider the effect of temperature on these properties. As the temperature changes, the physical and chemical properties of the ceramic material can also change, which can affect the dielectric, electrical, and impedance properties.

When cooling the furnace from high temperature to low temperature, the properties of the ceramic material may not behave in exactly the same way as when heating the furnace from low temperature to high temperature. This is because the cooling process can lead to the formation of defects or changes in the crystal structure of the ceramic material, which can affect the dielectric, electrical, and impedance properties.

The nature of the plot of the dielectric, electrical, and impedance properties may also be affected by the cooling process. For example, if the cooling process leads to the formation of defects or changes in the crystal structure, the nature of the plot may change, and some minor differences may occur in the values of the properties.

However, the extent of the changes in the properties and the nature of the plot will depend on several factors, such as the composition and microstructure of the ceramic material, the cooling rate, and the temperature range. Therefore, it is important to carefully analyze and compare the data obtained during heating and cooling to understand the effect of temperature on the dielectric, electrical, and impedance properties of the ceramic material.

I agree with Dr. Khaled Abdelkarem

But I also want add some thoughts. Are you sure that when you do your experiment your temperature chamber heated on full volume equally. Is thermocouple measuring temperature near the sample?

When you measure impedance or permittivity during cooling of themperature chamber you probably get more accurate data because test sample and surrounded area have the same temperature. During the heating of test chamber it is possible that sample (especially when it has low coefficient of thermal conductivity) has lower temperature comparing to what thermocouple shows. It needs some time to stabilize temperature and heat the test sample before measurement.