DIELECTRIC BEHAVIOR IN THE SYSTEMS PbHfO$sub 3$-BaHfO$sub 3$ AND PbHfO$sub 3$-SrHfO$sub 3$

Journal Article · Sun Apr 01 00:00:00 EST 1962 · Dissertation Abstr.

OSTI ID:4806457

Wilcox, D L

Phase transitions in the systems (Pb/sub x/Ba/sub 1-x/)HfO/sub 3/, where x varies from 1.00 to 0.60, and (Pb/sub gamma /Sr/bus 1- gamma /)HfO/sub 3/, where y varies from 1.00 to 0.80, were investigated by dielectric and structural measurements. The ceramic samples were prepared by conventional ceramic fabrication techniques from analytical grade raw materials. Alkaline earth carbonates and basic lead carbonate supplied the +2 valence metal rons and a high purity hafnium oxide (99.95% HfO/sub 2/) was the source of Hf/sup 4+/. The sample densifying, firing operation was accomplished in a lead oxide atmosphere to reduce volatilization. The dielectric behavior of the phases present in the two systenrs was studied by employing measurements of dielectric constant as a function of temperature, electric polarizability versus applied field, and x-ray techniques. Lead hafnate has two anomalies in the dielectric constant versus temperature curve which appear at 160 deg C and 208 deg C. The first anomaly represents a phase transition from the lower temperature, antiferroelectric, pseudotetragonal phase to the upper temperature, antiferroelectric, pseudotetragonal phase of another type. The second anomaly at 208 deg C is the temperature at which the upper antiferroelectric phase transforms to a cubic, paraelectric phase. The dielectric constant of ceramic PbHfO/sub 3/ is 120 at room temperature and about 2000 at 208/ deg C. Increasing barium additions in (Pb,Ba/sub 1-x/)HfO/sub 3/ decrease both transition temperatures which occur in PbHfO/sub 3/. A ferroelectric region was found in the (Pb/sub x/Ba/sub 1-x/)HfO/ sub 3/ system at room temperature with x > 0.60 but < 0.80. The c region at room temperature was determined to have a rhombohedral pseudo-cubic structure with alpha = 89 deg 54 . The morphotropic phase boundary between the upper temperature antiferroelectric phase and the ferroelectric phase in (Pb/sub x/Ba/ sub 1-x/)HfO/sub 3/ was determined to lie between the compositional limits where x < 0.90 but >0.85, depending on the temperature. In the system (Pb gamma Sr/sub 1- gamma )HfO/sub 3/, strontium additions reduced the lower phase transition temperature. Small additions (~5%) of strontium caused a slight increase in the upper phase transition temperature of lead hafnate but further additions reduced the transition temperature. An additional phase transition was observed at a temperature which was above the upper antiferroelectric transition temperature of PbHfO/sub 3/. The temperature of the new phase transition increased as the amount of strontium in (Pb/sub gamma /Sr/sub 1- gamma /)HfO/sub 3/ increased. The two non-polar phases in the (Pb,Sr)HfO/sub 3/ system which corresponded to those which ocour in PbHfO/sub 3/ were probably antiferroelectric whereas the new phase which was observed could be explained as erther a para electric or an antiferroelectric phase. A determination of the room temperature c/a axis ratio of PbHfO/sub 3/ and its pseudotetragonal solid solutions with BaHfO/sub 3/ and SrHfO/sub 3/ rndicated that the magnitude of the ratio was related to the upper phase transition temperature. In the (Pb,Ba)HfO/sub 3/ system, the c/a ratio increased from 0.988 for PbHfO/sub 3/ to 0.994 for Pb/sub 0.80/Ba/sub 0.20/HfO/ sub 3/ as the ratio rnoreased the upper phase transition temperature decreased. In the (Pb,Sr)HfO/sujb 3/, the c/a ratio remained nearly constant for small strontium additions and then increased toward unity. The delay in the change of the ratio corresponded with the slight increase rn the upper phase transition temperature. It was believed that as the c/a axis ratro of the room temperature pseudotetragonal phase approached unity, less thermal energy was required to cause a transformation to the higher symmetry phase which resulted in the observed decrease in the upper transrtron temperature.

• Research Organization: Univ. of Illinois, Urbana
• NSA Number: NSA-16-023688
• OSTI ID: 4806457
• Journal Information: Dissertation Abstr., Vol. Vol: 22; Other Information: Orig. Receipt Date: 31-DEC-62
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CHEMISTRY
ACIDITY
ALKALINE EARTH METALS
ANTIFERROELECTRICITY
BARIUM OXIDES
CARBONATES
CERAMICS
COMPACTING
CRYSTALS
DIAGRAMS
DIELECTRICS
ELECTRIC CONDUCTIVITY
ELECTRIC FIELDS
ENERGY
EVAPORATION
FABRICATION
FERROELECTRIC MATERIALS
FERROMAGNETIC MATERIALS
HAFNIUM OXIDES
HEAT TREATMENTS
HEATING
LATTICES
LEAD CARBONATES
LEAD HYDROXIDES
LEAD OXIDES
MEASURED VALUES
PARAELECTRICITY
PHASE DIAGRAMS
PREPARATION
SAMPLING
SINTERING
SOLID SOLUTIONS
STRONTIUM OXIDES
TEMPERATURE
X RADIATION