ELECTRICAL AND THERMAL MEASUREMENTS ON FE-AFE PHASE TRANSITIONS IN LEAD HAFNATE TITANATE COMPOSITIONS. Final Report
Electrical and Thermal Measurements. Investigations have been carried out to determine the characteristics of ferroelectric and antiferroelectric transitions in lead perovskites. Materials studied include solid solutions of lead zirconate titanate, lead zirconate titanate stannate, and lead hafnate titanate. These solid solutions were chosen because compositions among them possess a ferroelectric-to-antiferroelectric transition with rising temperature while others display an antiferroelectric-toferroelectric transition under the same conditions. Dielectric constant and loss were determined as functions of temperature and applied electric field, with an emphasis being placed on the use of loss conductance rather than tan delta as a method of examining the loss mechanisms in these materials. By this technique, the variation of transition temperature with external electric field was determined. The decrease of peak dielectric constant with external field characteristic of dielectric saturation was found to be especially prominent in transitions involving a ferroelectric phase. Hysteresis measurements were made primarily in an effort to separate the antiferroelectric double loop behavior from the normal ferroelectric loops near transitions. It was found that parts of some samples retained ferroelectric character many degrees above the normal transition temperature. Measurements of specific heat as a function of temperature were used to determine the relative free energies and entropies of the phases. From the results of these studies it appears that the reversal of transition direction mentioned above results from very slight shifts in the relative magnitudes of the free energy and the entropy of the ferroelectric and antiferroelectric phases of these materials, rather than from some wide change in their structural or chemical character. Dispersion of Dielectric Characteristics. The frequency dependence of the dielectric parameters of some polycrystalline materials exhibiting ferroelectricity and/or antiferroelectricity was examined under varying conditions of temperature and static electric field. Work was performed in the frequency range from 10/sup 2/ to 10/sup 5/ cps on lead zirconate stannate titanate and lead hafnate tithnate solid solutions. The dielectric constant and equivalent conductance'' were determined over a range of temperatures extending from 20 deg C to 200 deg C and up to field strengths of 8 kv/cm although the most extensive measurements were made at room temperature and zero fteld. Both ferroelectric and antiferroelectric phases of the materials were investigated and the trends of the results compared. The samples in general showed a loglinear decrease in dielectric constant with increasing frequency. The antiferroelectric samples displayed a decrease approximately one-third to one-haif that of the ferroelectric materials. For all samples, the equivalent conductance values plotted on a log-log scale against frequency yielded a straight line with a slope of very nearly one, suggesting the presence of hysteresis-type losses. These variations with frequency could be altered in various degree by changing temperature or field. Using as a basis the apparert hysteresis-type loss mechanism, a model is proposed which explains the equivalent conductance results and also remains consistent with the dispersion in the dielectric constant. The model involves the concept of minute polarization reversals by domain wall motion. The results at varying temperatures and field strengths are also incorporated into the model. The experimental findings for both the ferroelectric and antiferroelectric compositions show a great deal of consistency with the model, and with this as a foundation, it is suggested that perhaps the solid solution samples are neither purely ferroelectric nor purely antiferroelectric but rather a combination of the two phases with one more dominant. (auth)
- Research Organization:
- Oklahoma State Univ., Stillwater, OK. Research Foundation
- Sponsoring Organization:
- US Atomic Energy Commission (AEC)
- DOE Contract Number:
- AT(29-1)-789
- NSA Number:
- NSA-18-018458
- OSTI ID:
- 4037545
- Report Number(s):
- SC-DC-64-344
- Resource Relation:
- Other Information: For Sandia Corp., Albuquerque, N. Mex. Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANTIFERROELECTRICITY
COUPLING
CRYSTALS
DIAGRAMS
DIELECTRICS
DIFFRACTION
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRIC FIELDS
ELECTRICITY
ENERGY
ENERGY LEVELS
ENTROPY
FERROELECTRIC MATERIALS
FERROMAGNETIC MATERIALS
FREE ENERGY
FREQUENCY
GAMMA RADIATION
HAFNIUM COMPOUNDS
HYSTERESIS
INTERACTIONS
LEAD
LEAD COMPOUNDS
LOSSES
MATHEMATICS
MEASURED VALUES
MOTION
NUCLEAR MODELS
NUCLEAR THEORY
NUCLEI
NUCLEONS
POLARIZATION
QUANTITATIVE ANALYSIS
SOLID SOLUTIONS
SPECIFIC HEAT
SPIN
TEMPERATURE
THERMODYNAMICS
TIN COMPOUNDS
TITANIUM OXIDES
TRANSIENTS
TRANSITIONS
VARIATIONS
ZIRCONIUM COMPOUNDS