2 research outputs found
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Effect of Different Electrode Configurations on the Ultrafast Photoinduced Strain of Ferroelectric Devices
Ferroelectric materials possess switchable polarization that can be controlled by the application of an external electric field. Ferroelectrics also display piezoelectricity and generate surface charges upon applied strain or vice versa. Upon optical illumination, the photoinduced charge carriers migrate towards the spontaneous polarization exhibiting photovoltaic effect. By combining the photovoltaic and piezoelectric effects, ferroelectric materials generate ultrafast non-thermal photoinduced strain through optical excitation known as photostriction. Recent studies have shown that the photostrictive response of the ferroelectric devices can be tuned by controlling their initial polarization state. The work presented in this thesis aims to study the effect of different electrode configurations on the ultrafast photoinduced strain of ferroelectric devices. Pb[Zr0.2Ti0.8]O3 (PZT) / SrRuO3 (SRO)/ SrTiO3 (STO) and PZT/ LaSrMnO3 (LSMO) /STO heterostructures were grown using pulsed laser deposition (PLD) and were capped with indium tin oxide (ITO)/ Pt top electrodes to form ferroelectric devices in a capacitor geometry. Time-resolved x-ray diffraction was used to study the structural evolution of ferroelectric devices with different polarization histories in order to disentangle and compare the piezoelectric and photostrictive response in this system.
Both piezoelectric and photostrictive responses of the Pt/PZT/SRO/STO device over a range of applied voltages displayed two distinct remnant states and resembled an inverted butterfly loop indicating hysteretic behavior. Interestingly, photoinduced strain was observed to be a maximum near voltages where the film has the lowest tetragonality. A shift in piezoelectric response was also observed after irradiating the samples, which is likely due to a laser-induced field during our time-resolved studies. Similar studies on a different ITO/PZT/LSMO/STO device revealed that both the piezoelectric and photostrictive responses of the devices are altered by the different electrode configuration
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Behavior of soda-lime silicate glass under laser-driven shock compression up to 315 GPa
Shock experiments give a unique insight into the behavior of matter subjected to extremely high pressures and temperatures. Understanding the behavior of materials under such extreme conditions is key to modeling material failure and deformation dynamics under impact. While studies on pure silica are extensive, the shock behavior of other commercial silicates that contain additional oxides has not been systematically investigated. To better understand the role of composition in the dynamic behavior of silicates, we performed laser-driven dynamic compression experiments on soda-lime glass (SLG) up to 315 GPa. Using the accurate pulse shaping offered by the long pulse laser system at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLG was shock compressed along the Hugoniot to multiple pressure-temperature points. Velocity Interferometer System for Any Reflector was used to measure the velocity and determine the pressure inside the SLG. The U s -u p relationship obtained agrees well with the previous parallel plate impact studies. Within the error bars, no transformation to the crystalline phase was observed up to 70 GPa, which is in contrast to the behavior of pure silica under shock compression. Our studies show that the glass composition strongly influences the shock compression behavior of the silicate glasses