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dc.contributor.advisorKatiyar, Ram S.
dc.contributor.authorBhattarai, Mohan K.
dc.description.abstract<p>The thesis presents the studies of pure lead zirconate titanate <em>PbZr</em><sub>0.53</sub><em>Ti</em><sub>0.47</sub><em>O</em><sub>3</sub> (PZT) and lanthanum and scandium co-doped PZT ceramics synthesized by solid-state reaction method and thin films fabricated via pulse laser deposition technique. We synthesized PZT and (<em>PbZr</em><sub>0.53</sub><em>Ti</em><sub>0.47</sub>)<sub>0.90</sub>(<em>La</em><sub>x</sub><em>Sc</em><sub>1&minus;x</sub>)<sub>0.10</sub><em>O</em><sub>3</sub> (PL10x) where 0.0 &le; <em>x</em> &le; 0.8.<br /> <br /> The XRD patterns analyzed by Rietveld refinement indicate that PZT and PL10x ceramics are polycrystalline and exhibit well-defined diffraction peaks of the perovskite phase suggesting tetragonal phase symmetry (P4mm) of crystal structure. These results corroborate the deconvoluted Raman spectra using the phonon function. The presence of E(TO) and A(TO) Raman bands in low-frequency modes and mid-frequency modes confirm the vibration of A-site (Pb/La) cations, and displacement of B-site ( Zr/Ti/Sc) cations and O atoms along with c -axis suggest the existence of ferroelectric ordering in compounds. The recorded EDX spectrums of ceramics confirm the presence of constituent elements (Pb, Zr, Ti, La, Sc, and O), along with their respective characteristic x-ray emission lines, and SEM images exhibit a well-defined granular structure with an average grain size &sim; 2 &mu;m.<br /> <br /> We designed metal ferroelectric metal capacitors of ceramics as Ag/PL10x/Ag for dielectric and ferroelectric measurements. Temperature-dependent dielectric permittivity (&epsilon;&prime;) exhibits the diffuse phase transition (DPT) behavior enhanced on increasing lanthanum contents, which also decreases the ferroelectric phase transition temperature. Analyzing DPT for the highest content of lanthanum (PL8) by modified Curie-Weiss results 1 &le; <em>&gamma;</em> &le; 2 supports the peak broadening of material composition and confirms the existence of relaxor properties.<br /> <br /> Room temperature polarization-electric field (P-E) loops of Ag/PL10x/Ag ceramic capacitors confirm ferroelectricity. The P-E loops, suggest the normal ferroelectric behavior with enhanced polarization for lower contents of lanthanum. However, the higher content of lanthanum provides the slim loop hysteresis, which is the typical property of relaxor ferroelectric material. These results support the dielectric behavior of capacitors. We calculated the energy storage performance of the PL8 capacitor. It provides a higher recoverable energy density (<em>U</em><sub>re</sub>) &sim; 1162 mJ/cm<sup>3</sup> with an efficiency (<em>&eta;</em>) of &sim; 79 %. These obtained results provide that lanthanum and scandium co-doped ceramic capacitors are potential candidates for ferroelectric memory and energy storage applications.<br /> <br /> PZT and PL10x thin films were fabricated on top of a buffer layer of LSMO (<em>La</em><sub>0.67</sub><em>Sr</em><sub>0.33</sub><em>MnO</em><sub>3</sub>) on MgO (100) substrate using the PLD technique. The X-ray diffraction peaks show a single-phase perovskite structure of thin films with a preferred (100) orientation that coincides with the MgO and tetragonal phase symmetry (P4mm) corroborating the ceramics sample. Further, we analyzed the peak broadening of XRD peaks by Williamson and Hall&rsquo;s (W&ndash;H) method. It suggests that peak broadening occurs on the doping samples, which increases on increasing lanthanum compared to scandium might be due to higher atomic radii of lanthanum compared to scandium. AFM images exhibit surface roughness increases for a higher content of lanthanum thin films due to an increase in peak broadening supporting the crystal size analysis by the W-H method. The analysis of Raman spectra further confirms the structural stability and ferroelectric ordering of thin-film capacitors.<br /> <br /> We deposited Pt at the top of grown thin films to design metal ferroelectric metal capacitors as Pt/PZT/LSMO and Pt/PL10x/LSMO for dielectric and ferroelectric measurements. The temperature-dependent ϵ &prime; shows the strong frequency dependency for the PL0, PL6, and PL10x thin film capacitors. The analysis of ferroelectric behavior by Curie-Weiss&rsquo;s law exhibits the degree of deviation from the Curie-Weiss law i.e; ∆T<sub>m</sub> on doped thin films. It provides the value of ∆T<sub>m</sub> &sim; 15K, 90K, 50K, and 70K for PZT, PL0, PL6, and PL8 respectively due to compositional induced diffuse phase transition behavior. The DPT of PL0, PL6, and PL8 capacitors were further analyzed by a modified Curie-Weiss law. It yields (1 &le; <em>&gamma;</em> &le; 2) indicating that these thin-film capacitors exhibit incomplete diffuse phase transition (DPT) on those material compositions. The reasonably well-fitted non-linear curve using the Vogel-Fulcher relation further confirms the relaxor behavior of materials.<br /> <br /> The polarization-electric field (P-E) loops of thin-film capacitors support ferroelectricity. It shows typical ferroelectric loops with enhanced polarization and reduced coercive field for PL2, and PL4 thin films. However, PL0, PL6, and PL8 capacitors attribute slim loop hysteresis suggesting a relaxor ferroelectric nature. The PL0 and PL6 thin films show a better spontaneous polarization (<em>P</em><em><sub>S</sub></em>). We examined the energy storage capacity and efficiency of these thin films using unipolar P-E loops. The superior energy stored performance were achieved on PL0 and PL8 thin film capacitors which yielded <em>U</em><sub>re</sub> = 54.63 J/cm<sup>3</sup> and 26.4 J/cm<sup>3</sup> with &eta; &sim; 70.22 % and 66 % respectively.</p>en_US
dc.description.sponsorshipI am pleased to acknowledge different funding institutions that provided financial support during my Ph.D. such as Decanato de Estudios Graduados e Investigación (DEGI), NASA EPSCoR, DoD, and NSF.en_US
dc.rightsAttribution-NonCommercial-NoDerivs 3.0 United States*
dc.subjectDiffuse phase transition (DPT)en_US
dc.subjectEnergy storage densityen_US
dc.subjectPulse laser depositionen_US
dc.subjectRare-earth elementsen_US
dc.subjectRelaxor ferroelectricen_US
dc.subjectSolid-state methoden_US
dc.subjectVogel-Fulcher relationen_US
dc.subject.lcshLead zirconate titanateen_US
dc.subject.lcshRaman spectroscopyen_US
dc.titleInvestigations on rare earth doped lead zirconate titanate for energy storage applicationsen_US
dc.rights.holder© 2022 Mohan K. Bhattaraien_US
dc.contributor.committeeMorell, Gerardo
dc.contributor.committeeWeiner, Brad R.
dc.contributor.campusUniversity of Puerto Rico, Río Piedras Campusen_US
dc.description.graduationSemesterSummer (3rd Semester)en_US
dc.description.graduationYear2022en_US in Chemical Physics, Department of Physicsen_US

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