Lab III: Physical Properties of Materials
By Will Paxton
The electrical properties of 5 different samples were studied. Characterization of these samples was through the dielectric properties, as this is a very important step. The capacitance was measured for each sample incrementally while heating them up to 135ºC. In a second part to the experiment, piezoelectric samples were studied, and their piezoelectric coefficient was calculated.
The objective of the experiment was to measure and interpret dielectric constants for 5 known materials. The ceramics used were Al2O3, AlN, PZT, SiO2 glass, and BeO. In order to determine the dielectric constant, a GenRad 1689 Digibride RLC apparatus was used to measure the capacitance. When a dielectric material is placed between the plates of a capacitor, an increase of charge storage capacity is expected. This is due to the polarization within the dielectric material itself, aiding in storing the charge at the plates. The methodology of the experiment was simple and straightforward. First off, the geometry was determined for all of the ceramics by measuring the thickness and plate area. Once the apparatus was calibrated, their capacitance was measured at 1 KHz, 10 KHz, and 100 KHz. Lastly, the ceramics were placed on a multi-sample holder and inserted into an oven. While the samples were heated to 135ºC, the capacitance was measured 10 steps along the way. It was expected that the dielectric constant of the ceramics would increase proportionally to the increase of temperature. Another separate objective of the experiment was to measure and interpret the piezoelectric coefficients of 3 known piezoelectric materials. The piezoelectrics used in the experiment were 840, 850, and 880. The piezoelectric coefficient was simply measured using a Pennebaker Model 8000 Piezo d33 Tester. The Piezo tester applies a pressure to the sample which, in turn, generates a charge. By utilizing a variable capacitor, an AC voltage is obtained from Q = CV. The AC voltage is then measured on a Digital Multi-Meter with a value equal to X 10-12 C/N. It was expected that the readings from the Piezo tester were to be close, if not equal, to the given values.
The samples were measured for thickness (d) and area (A). The micrometer used was old, and an offset of .005 in was observed. All data was corrected for this offset and was converted to centimeters for calculations.
Table 1. Capacitor geometry
materialmeasured thicknessactual thicknessd, thicknessA, area
in, inchesin, inchescm, centimeterscm2, square centimeters Al2O30.02050.01550.039376.25
Table 2. Dielectric constants measured for multiple frequencies Material1 KHz10 KHz100 KHz
κ, Dielectric Constant κ, Dielectric Constant κ, Dielectric Constant Al2O30.8630.9580.950
Table 3. Dielectric constants of heated samples
º Cκ, Dielectric Constant κ, Dielectric Constant κ, Dielectric Constant κ, Dielectric Constant κ, Dielectric Constant 266.5836.527352.9790.1796.398
Below are two figures for Dielectric Constant (κ) versus Temperature. The data for PZT is included on a separate graph because is it much higher than the others. This was to optimize readability of the graphs by grouping those...