Structural and thermodynamic investigation of the ferroelectric phase transition in lanthana-substituted lead titanate

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7114802

Rossetti, Jr, G A

The structural and thermodynamic properties of the perovskite-structured solid solution between lead titanate and the defect compound lanthanum titanate have been investigated. The end member lead titanate is representative of a large family of oxygen octahedra ferroelectrics that undergo discontinuous phase transitions from a centrosymmetric cubic prototype (Pm3m) to a tetragonal ferroelectric phase (P4mm) of the type commonly characterized by the condensation of a Brillouin zone-center polar lattice vibrational model. The aliovalent substitution of lanthanum (III) for lead (II) induced tricritical-like behavior and diffuses the phase transition. A series of well crystallized, chemically derived powder specimens were prepared. The temperature variation of the order parameter (spontaneous polarization) through the transition was measured indirectly by diffraction methods via the coupling to the spontaneous elastic strain. These data were combined with calorimetric data and used to estimate the renormalization of the relevant parameters of the thermodynamic potential as a function of the extent of lanthanum doping within the quasi-homogeneous approximation of the Landau-Devonshire theory. Detailed structural information was obtained on selected compositions using X-ray line profile analysis, transmission electron microscopy, and powder neutron methods. The results suggested that a systematic complication of the ferroelectric domain structure was responsible for the anomalous dielectric behavior. The role played by composition fluctuations, heterophase fluctuations, extended defects, and/or additional lattice instabilities appeared to be secondary. When interpreted within the theoretical framework of the Landau-Devonshire formalism, the breakdown of the conventional first-order phase transition behavior was primarily associated with changes in the elastic contributions to the thermodynamic potential.

• Research Organization: Pennsylvania State Univ., University Park, PA (United States)
• OSTI ID: 7114802
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204 -- Ceramics
Cermets
& Refractories-- Physical Properties
ALLOYS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
CUBIC LATTICES
DISPERSIONS
FERROELECTRIC MATERIALS
INTERMETALLIC COMPOUNDS
LANTHANUM COMPOUNDS
LEAD COMPOUNDS
MIXTURES
OXYGEN COMPOUNDS
PEROVSKITES
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
SOLID SOLUTIONS
SOLUTIONS
TETRAGONAL LATTICES
THERMODYNAMIC PROPERTIES
TITANATES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS