Explanation of Polarization Measurement:

1. Development and Implementation of a Polarization Measurement System Cassandra Llano, Elena Aksel, Anderson D. Prewitt, ShrutiBanavaraSeshadri, Jennifer Forrester and Jacob L. Jones Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA • Explanation of Polarization Measurement: Polarization vs. Electric Field: Objective: To develop a device that can accurately measure the polarization of materials at various electric fields and frequencies in order to acquire a better understanding of the structure-property relationships in piezoelectric materials. • Sawyer-Tower Circuit • To measure polarization, a Sawyer-Tower circuit is used • The voltage is cycled by the function generator in a specific waveform • The reference capacitor and the sample are in series, so the voltage across the reference capacitor is measured • Thus the charge on the sample (polarization) can be measured by: • Q= C x V • Where Q is charge, C is capacitance, and V is voltage • Surface Charge = (C x V)/surface area of sample • We can show the polarization of a material in an oscillating electric field by plotting the electric field applied to the material on the x-axis, and the polarization of the material on the y-axis Sm doped PZT Pb0.97Sm0.02Zr0.45(TiO3)0.55 Pb0.97Sm0.02Zr0.3(TiO3)0.7 Pb0.97Sm0.02Zr0.2(TiO3)0.8 Pb0.925Sm0.05Zr0.2(TiO3)0.8 Polarization (pC/cm2) Motivation: Polarization of a piezoelectric material gives insight into many of its structure-property relationships, for example the permittivity is directly proportional to polarization. An apparatus that measures polarization will provide an avenue to comprehend these properties. Electric field (kV/mm) • Compare hysteresis loops of 2% and 5% Sm doped PZT at different Zr/Ti ratios • Pb0.97Sm0.02Zr0.2(TiO3)0.8 shows conductivity in the sample The point of polarization saturation, Ps where the maximum amount of domains in the sample are aligned in the direction of the field. The remnant polarization, Prleft on the sample at zero field. Oscilloscope NBT with BT Solid Solutions Na0.5Bi0.5TiO3 0.96(Na0.5Bi0.5TiO3) 0.04(BaTiO3) 0.94(Na0.5Bi0.5TiO3) 0.06(BaTiO3) 0.93(Na0.5Bi0.5TiO3) 0.07(BaTiO3) 0.91(Na0.5Bi0.5TiO3) 0.09(BaTiO3) 0.87(Na0.5Bi0.5TiO3) 0.13(BaTiO3) Reference Capacitor Earth Piezoelectric Sample Set-Up: The polarization apparatus, probe and platform was placed in a plexi-glass cage, which has a safety on-off sensor that only permits the high voltage to run if the cage door is closed (Figures 1 and 2). Polarization (pC/cm2) Function Generator Figure 5. Sawyer-tower circuit diagram The coercive field, Ec is the points where domain switching starts to occur. Electric field (kV/mm) • Compositions made by Dr. Forrester in Dr. Jacob Jones’ lab • NBT and NBT-9BT show some conductivity in the samples Figure 6. Example of Sawyer-tower reference capacitor Figure 1. Polarization apparatus with cage Figure 7. Polarization Vs. Electric Field NBT with BT Solid Solutions • The function generator allows the user to select the specific wave functions (sine, square, triangular), as well as the voltage and frequency that needs to be applied to the sample (Figure 3 top). • The voltage amplifierreceives the signal from the function generator and sends the appropriate voltage/frequency to the probe on the sample (Figure 3 bottom). • The oscilloscopeshows the applied wave function and the response from the sample (Figure 3 middle). • Experimental: • The following samples were tested in the PE set up: Sm-doped lead zirconatetitanate (PZT) and sodium bismuth titanate (NBT) with barium titanate (BT) solid solutions • The measurements were done using a triangular waveform at 1 Hz. • All samples were cycled at incremental electric fields, starting from a low field, until a full PE loop was observed. • Experimental: • The following samples were tested in the PE set up: Sm-doped lead zirconatetitanate (PZT) and sodium bismuth titanate (NBT) with barium titanate (BT) solid solutions • The measurements were done using a triangular waveform at 1 Hz. • All samples were cycled at incremental electric fields, starting from a low field, until a full PE loop was observed. 0.94(Na0.5Bi0.5TiO3) 0.06(BaTiO3) 0.93(Na0.5Bi0.5TiO3) 0.07(BaTiO3) 0.91(Na0.5Bi0.5TiO3) 0.09(BaTiO3) 0.88(Na0.5Bi0.5TiO3) 0.12(BaTiO3) Polarization (pC/cm2) Electric field (kV/mm) Conclusions: • Compositions made by Dr. Wook Jo’s in Darmstadt, Germany • 0.91(Na0.5Bi0.5TiO3) 0.09(BaTiO3) had large conductivity Figure 2. platform, probe and holder • Built a set-up that measures polarization with the following capabilities: • Sm-doped PZT at the Morphotropic phase boundary has a lower Ec than rhombohedral PZT • The addition of Sm to a PZT sample with a .2/.8 Zr/Ti ratio decreases sample conductivity • Samples prepared in the J. Jones lab showed comparable property results to those from Darmstadt, Germany • The addition of 6-7 mol% BT to NBT significantly reduces Ec while Maintaining Pr Future Work: • Setting up alinear variable displacement transducer (LVDT) • The LVDT will be able to measure the strain as well as the polarization of a sample at the same time Figure 3. Function generator, Oscilloscope andVoltage amplifier (top to bottom) Figure 8. LVDT References: http://www.doitpoms.ac.uk/tlplib/ferroelectrics/printall.php?question=4&type=1Acknowledgments: Research Experience in Materials (REM) ; Howard Hughes Medical Institute- Science for Life Program; NSF award #DMR-0746902 ; U.S. Department of the Army award # W911NF-09-1-0435