Impedance Spectroscopy for Detecting Phase Transitions in KBr
Team members
Laphas Precmcharoen, Song Runlin, Gao Jia
Introduction
This project aims to study the electrical properties of Potassium Bromide (KBr) using impedance spectroscopy.
Materials
1. Electrochemical Impedance Spectroscopy (EIS) System
2. KBr samples
3. Two-electrode system
4. Frequency generator
Procedure
Palletizing KBr
To prepare the KBr for impedance spectroscopy, the powdered KBr was first palletized. This process involved grounding the KBr into powder and then compressing under a pressure of approximately 5 tons using a hydraulic press for approximately 3 minutes, forming a compact, disk-shaped pellet with a diameter of 11.4 mm and a thickness of approximately 2.61 mm. The uniform size and shape of the pellet were crucial for ensuring consistent and reliable impedance measurements.
Application of Silver Paint
After palletization, both sides of the KBr pellet were coated with a thin layer of silver paint. This step was performed carefully to ensure a uniform conductive layer was formed, minimizing any potential impedance contributions from uneven surface conductivity. The silver-coated pellet was then left to dry for 15 minutes, ensuring the paint was fully set and conductive.
Electrode Setup
Once the silver paint was dry, electrodes were attached to both sides of the pellet. This setup facilitated the application of an alternating current (AC) through the pellet, necessary for impedance measurements. The electrodes were connected to the impedance spectroscopy system.
Impedance Spectroscopy System and Heating
The impedance spectroscopy measurements were conducted using an impedance analyzer capable of capturing impedance data over a broad frequency range. The frequency range for the measurements spanned from 100 Hz to 100,000 Hz, with a total of 60 frequencies measured at evenly spaced logarithmic intervals. This comprehensive frequency range was selected to ensure a detailed characterization of the KBr pellet's impedance properties across different electrical conduction regimes. For the experiment, the KBr pellet, with electrodes attached, was placed in a temperature-controlled chamber within the impedance spectroscopy system. The temperature of the chamber was increased in steps of approximately 10°C, starting from 50°C and reaching up to 250°C. At each temperature step, impedance data were recorded across the predetermined frequency range. This methodical temperature increment allowed for the detailed observation of the KBr pellet's phase transition behavior at each step.
Data Analysis
Impedance data were analyzed and presented as Nyquist plots for each temperature step. Circle fitting techniques were employed on these plots to deduce the conductivity and capacitance values across the temperature spectrum. The analysis focused on both the conductivity times temperature ((σT)) versus reciprocal temperature ((1/T)) graph and the log(σ) versus reciprocal ((1/T)) temperature graph. These analyses aimed to identify shifts in the slopes of these graphs, which are indicative of phase transitions within the KBr pellet. Special emphasis was placed on changes observed around 180°C, where a noticeable shift in the slopes suggested a phase transition.
Results and Discussions
Conclusion
Timeline
| 5/3 | Learn how to do the Impedance spectrocopy and how to palletize samples | |
| 7/3 | Palletize powdered KBr | |
| 12/3 | Patelletize KBr into different thicknesses | |
| 14/3 | Silver paint both sides of the pallets | |
| 19/3 | 1st attempt on the impedance spectroscopy across different temperatures | |
| 20/3 | final attempt on the impedance spectroscopy across different temperature from 50C - 255C of the pallet with diameter 11.4 mm and thickness 2.61 mm | |
| 21/3 | Do the impedance spectroscopy while applying bias DC voltage from 0V to 5V of the pallet with diameter 11.7 mm and thickness 3.54 mm and do the impedance spectroscopy on the pallets with different thicknesses | |
| 26/3 | Fit the nyquist plot of the temperature data with a semi circle to get approximated resistance and capacitance | |
| 2/4 | Discuss the result and fit the DC dependent data with semi circle | |
| 4/4 | Analyze the data and discuss | |
| 9/4 | Discuss the possible mechanism of phase transition and updating wiki page |