DISPERSION AND DISTRIBUTION OF OPTICAL INDEX OF REFRACTION IN FERROELECTRIC RELAXOR CRYSTAL

Open Access
Author:
Li, Chunlai
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 16, 2005
Committee Members:
  • Ruyan Guo, Committee Chair
  • Amar S Bhalla, Committee Chair
  • Leslie Eric Cross, Committee Member
  • William Blaine White, Committee Member
  • Shizhuo Yin, Committee Member
Keywords:
  • PBN
  • transmission
  • birefringence
  • refractive index
  • optical properties
  • relaxor ferroelectics
  • polar region
  • FTIR
  • PZN-PT
Abstract:
This thesis deals with the optical properties of relaxor ferroelectrics with nano/micro polar regions, including their optical frequency dispersion near phase transition, thermo-optical properties, and transmission spectrum analysis. The essential objectives of this thesis work are to deepen the understanding on diffuse phase transition of relaxor ferroelectrics and to obtain practical data for potential optical application from technically important ferroelectrics crystals PBN and PZN-PT. Temperature dependent birefringence and optical refractive indices of PBN (Pb1-xBaxNb2O6) crystal (1-x=0.57) were measured in several optical wavelengths (ƒÜ= 694nm, 633nm, 535nm, and 450nm) to understand the optical frequency dependency of ferroelectric phase transitions in relaxor ferroelectric crystals of tungsten bronze structure. Local polarization is verified to be dynamically activated by thermal process and probed effectively by suitable wavelength of light. An optical isotropic point, as a function of temperature and light frequency, is reported at which the crystal¡¦s standing birefringence is fully compensated by polarization. A modified single oscillator model is used to calculate the index of refraction in the ferroelectric phase. The deviation temperature from the single oscillator model is reported to be significantly marking the crossover from macroscopic to microscopic polarization. A new parameter, optical Curie temperature region, defined by the temperature difference between the well known Burns temperature and the deviation temperature (from the single oscillator model for index of refraction) is explored for its significance in depolarization behavior of the micro- to nano-polar regions of the ferroelectric relaxor. Temperature dependent optical indices of refraction of PZN-0.12PT (1-x)PbZn1/3Nb2/3O3-xPbTiO3, x=0.12, were also studied with emphasis on poling effect. The refractive index n3 decreases as a result of [001] poling. Temperature dependent effective energy of dispersion oscillator and dispersion energy were calculated using single oscillator model and found that and increased by 32% and 60% after [001] poling, respectively. Birefringence of poled PZN-0.12PT also was measured with several frequencies and varying temperature. The polarization derived from refractive index and birefringence were consistent with each other. The remnant polarization was increased by approximately 30% as a result of [001] poling. Transmission spectrum of PZN-0.12PT was measured from near UV to IR for both poled sample and unpoled sample. Transmission was improved significantly after poling. By analyzing the transmission spectrum in the visible range, optical band gap and lattice phonon were determined. The existence of hydrogen in PZN-0.12PT single crystal grown by flux method was postulated based on evidence obtained by FTIR. For accurate and fast birefringence measurement, which is of fundamental importance to device design, quality control, and various sensing functions, a two-dimensional birefringence profiling and analysis system was designed and implemented successfully. Jones matrices of two and three 90 degree domains are derived and conclude that odd number of stacked 90„a domains can be treated as a single 90 degree domain while even number of stacked 90 degree domains can be treated as two 90 degree domains. By rotating analyzer method a test experiment using voltage controllable liquid crystal as sample is demonstrated.