Maureen L. Mulvihill

The Role of Processing Variables in the Flux Growth of Lead Zinc Niobate-Lead Titanate Relaxor Ferroelectric Single Crystals

Relaxor ferroelectric single crystals of Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN-PT) are of interest as high performance transducers due to their very large piezoelectric coupling and dielectric properties. A high temperature flux solution method was used to grow (1- x)PZN-( x)PT, where x= 0.0, 0.1 and 0.15 single crystals. Processing conditions were optimized to increase the size and yield of the perovskite crystals, including variation of the flux to composition ratio, cooling rate, soak time and soak temperature. The crystals varied in size from 0.01 cm to 1.5 cm on an edge, and in color from opaque to brown due to the changes in processing conditions. The crystals were characterized by XRD, dielectric constant and dielectric loss measurements. As the content of PT increased the transition from the paraelectric to the ferroelectric phase approached first order behavior and the crystal structure transformed from rhombohedral to tetragonal. This structure transition caused the lattice constant along the c-axis to elongate as the c/a ratio increased. At room temperature, the dielectric constants for the PZN-PT compositions along the [111] or [001] axes were as great as 5000 and the dielectric losses were as low as 0.01.

The Effect of Growth Conditions on the Dielectric Properties of Pb(Zn1/3Nb2/3)O3 Single Crystals

The effect of growth conditions on the dielectric properties and ferroelectric transition of perovskite Pb(Zn1/3Nb2/3)O3 single crystals was examined. Crystals were grown by the flux technique using PbO as a self flux. Increased cooling rate and soaking temperature resulted in a decreased Zn/Nb ratio, and corresponding increased temperature of the maximum dielectric constant (Tmax ), and decreased room temperature values of the dielectric constant and loss. Different crystal colors and quality were also associated with the various growing conditions. Although dielectric properties, domain stability after poling, and associated piezoelectric properties are a function of Tmax , it was shown that crystal quality was critical for the observed variation in these properties.

An X-ray diffraction study of superlattice ordering in lead magnesium niobate

We report a direct observation of the superlattice diffraction peaks, indicating a doubling of unit cell, from lead magnesium niobate (PMN) single crystal using X-ray diffraction technique. The broad width of the superlattice diffraction peaks indicates that the superlattice ordering in PMN is of short range. In the temperature range studied (from 10 K to 355 K) the peak width shows no temperature dependence. The intensity distribution among the observed superlattice peaks suggests that the doubling of unit cell in the superlattice regions involves significant ionic displacements in addition to a chemical ordering.

Dynamic motion of the domain configuration in relaxor ferroelectric single crystals as a function of temperature and electric field

Abstract Relaxor ferroelectrics exhibit unique characteristics such as a broad phase transition and frequency dispersion which may originate from the configuration of ferroelectric microdomains. In this study, the dynamic behavior of the macrodomains in Pb(Zn1/3Nb2/3)O3 single crystals was observed using an optical microscope in combination with a CCD camera system. Many domain characteristics such as changes in birefringence, transition between microdomains and macrodomains, and “freeze-in” temperature of the macrodomains were optically observed. These observations were then compared to measured dielectric properties in an attempt to clarify the relationship between the dielectric properties and the behavior of macrodomains.

Crystal growth and ferroelectric related properties of (1-x)Pb(A/sub 1/3/Nb/sub 2/3/)O/sub 3/-xPbTiO/sub 3/ (A=Zn/sup 2+/, Mg/sup 2+/)

Crystals of (1-x)Pb(A/sub 1/3/Nb/sub 2/3/)O/sub 3/-xPbTiO/sub 3/ (A=Zn/sup 2+/, Mg/sup 2+/) were grown by the flux technique. The dielectric and piezoelectric properties as a function of composition and crystal orientation have been evaluated. Both MPB and non-MPB crystals were found to possess high piezoelectric properties. Values of longitudinal electromechanical coupling coefficients (k/sub 33/)>90%, dielectric constants ranging from 3000 to 5000 with low dielectric loss <1% were observed for rhombohedral crystals. Tetragonal crystals with increased PbTiO/sub 3/ content exhibited large thickness coupling coefficients (k/sub T/)>63% with relatively low dielectric constant (/spl sim/1000). Ultrahigh values of piezoelectric coefficients (d/sub 33/)>2000 pC/N were also measured for non-MPB crystals and confirmed by direct E-field strain measurements. These properties are briefly discussed in relation to device performance.

Bulk photovoltaic effect for the linearly polarized light in Pb(Zn1/3Nb2/3)O3 single crystals

The bulk photovoltaic effect in non-centrosymmetric crystals is caused by asymmetric generation, recombination or scattering of excited nonequilibrium electronic carriers. In this paper, the photovoltaic effect has been investigated in relaxor ferroelectric Pb(Zn1/3Nb2/3)O3 single crystals using linearly polarized light. Angular dependence of photovoltaic voltage and current on the polarization direction of light was observed in the crystal. A phenomenological model was proposed to fit the experimental results from which the photovoltaic coefficients were calculated.