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Pressure as a probe of the physics of ABO{sub 3} relaxor ferroelectrics

Description: Results on a variety of mixed ABO{sub 3} oxides have revealed a pressure-induced ferroelectric-to-relaxor crossover and the continuous evolution of the energetics and dynamics of the relaxation process with increasing pressure. These common features have suggested a mechanism for the crossover phenomenon in terms of a large decrease in the correlation length for dipolar interactions with pressure--a unique property of soft mode or highly polarizable host lattices. The pressure effects as well as the interplay between pressure and dc biasing fields are illustrated for some recent results on PZN-9.5 PT,PMN and PLZT 6/65/35.
Date: February 14, 2000
Creator: SAMARA,GEORGE A.
Partner: UNT Libraries Government Documents Department

Pressure as a probe of the physics of relaxor ferroelectrics

Description: Pressure studies have provided new insights into the physics of compositionally-disordered ABO{sub 3} oxide relaxors. Specifically, results will be presented and discussed on a pressure-induced ferroelectric-to-relaxer crossover phenomenon, the continuous evolution of the energetic and dynamics of the relaxation process, and the interplay between pressure and electric field in determining the dielectric response.
Date: January 25, 2000
Creator: SAMARA,GEORGE A.
Partner: UNT Libraries Government Documents Department

Pressure as a Probe of the Physics of Relaxor Ferroelectrics

Description: Pressure studies have provided new insights into the physics of compositionally-disordered ABO{sub 3} oxide relaxors. Specifically results are presented and discussed on a pressure-induced ferroelectric-to-relaxor crossover phenomenon, the continuous evolution of the energetics and dynamics of the relaxation process, and the interplay between pressure and electric field in determining the dielectric response.
Date: August 9, 1999
Creator: Samara, George A.
Partner: UNT Libraries Government Documents Department

FWP executive summaries: basic energy sciences materials sciences and engineering program (SNL/NM).

Description: This report presents an Executive Summary of the various elements of the Materials Sciences and Engineering Program which is funded by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy at Sandia National Laboratories, New Mexico. A general programmatic overview is also presented.
Date: July 1, 2006
Creator: Samara, George A. & Simmons, Jerry A.
Partner: UNT Libraries Government Documents Department

Pressure-induced crossover from long-to-short-range order in [Pb(Zn{sub 1/3})Nb{sub 2/3}O{sub 3}]{sub 0.905}(PbTiO{sub 3}){sub 0.095} single crystal

Description: A pressure-induced crossover from normal Ferroelectric-to-Relaxer behavior has been observed in single crystal [Pb(Zn{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.905}(PbTiO{sub 3}){sub 0.0095}, or PZN - 9.5% PT. Analogy with similar observations for other perovskites indicates that this crossover is a general feature of compositionally-disordered soft mode ferroelectrics. The Pressure-Temperature phase diagram has been also determined.
Date: January 25, 2000
Creator: SAMARA,GEORGE A.; VENTURINI,EUGENE L. & SCHMIDT,V. HUGO
Partner: UNT Libraries Government Documents Department

The Dielectric Properties and Phase Transitions of [Pb(Zn{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.905} (PbTiO{sub 3}){sub 0.095}: Influence of Pressure

Description: Studies of the influences of temperature, hydrostatic pressure, dc biasing field and frequency on the dielectric constant ({epsilon}{prime}) and loss (tan {delta}) of single crystal [pb (Zn{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.905} (PbTiO{sub 3}){sub 0.095}, or PZN-9.5PT for short, have provided a detailed view of the ferroelectric (FE) response and phase transitions of this technologically important material. While at 1 bar, the crystal exhibits on cooling a cubic-to-tetragonal FE transition followed by a second transition to a rhombohedral phase, pressure induces a FE-to-relaxer crossover, the relaxer phase becoming the ground state at pressures {ge}5 kbar. Analogy with earlier results suggests that this crossover is a common feature of compositionally-disordered soft mode ferroelectrics and can be understood in terms of a decrease in the correlation length among polar domains with increasing pressure. Application of a dc biasing electric field at 1 bar strengthens FE correlations, and can at high pressure re-stabilize the FE response. The pressure-temperature-electric field phase diagram was established. In the absence of dc bias the tetragonal phase vanishes at high pressure, the crystal exhibiting classic relaxor behavior. The dynamics of dipolar motion and the strong deviation from Curie-Weiss behavior of the susceptibility in the high temperature cubic phase are discussed.
Date: August 1, 2000
Creator: SAMARA,GEORGE A.; VENTURINI,EUGENE L. & SCHMIDT,V. HUGO
Partner: UNT Libraries Government Documents Department

Optical properties of colloidal germanium nanocrystals

Description: Highly crystalline germanium (Ge) nanocrystals in the size range 2--10 nm were grown in inverse micelles and purified and size-separated by high pressure liquid chromatography with on-line optical and electrical diagnostics. The nanocrystals retain the diamond structure of bulk Ge down to at least 2.0 nm (containing about 150 Ge atoms). The background- and impurity-free extinction and photoluminescence (PL) spectra of these nanocrystals revealed rich structure which was interpreted in terms of the bandstructure of Ge shifted to higher energies by quantum confinement. The shifts ranged from {minus}0.1 eV to over 1 eV for the various transitions. PL in the range 350--700 nm was observed from nanocrystals 2--5 nm in size. The 2.0 nm nanocrystals yielded the most intense PL (at 420 nm) which is believed to be intrinsic and attributed to direct recombination at {Gamma}. Excitation at high energy (250 nm) populates most of the conduction bands resulting in competing recombination channels and the observed broad PL spectra.
Date: May 1, 2000
Creator: WILCOXON,JESS P.; PROVENCIO,PAULA P. & SAMARA,GEORGE A.
Partner: UNT Libraries Government Documents Department