PT Crystals Research Articles

Preparation of PbTiO 3 nanoceramics based on hydrothermal nanopowders and characterization of their electrical properties

In this work, we report the preparation of lead titanate (PT) nanoceramics (with an average grain size of ∼200 nm in diameter) by using hydrothermal PT nanoparticles as start materials and characterized the dielectric and ferroelectric properties. The dielectric constant of the ceramic was found to be ∼180 (at 1 kHz) at room temperature and reached a maximum value of 8330 at ∼490 °C, suggesting that the Curie temperature of the nanoceramics is consistent with the known value of PT crystals. Ferroelectric domains and hysteresis loops were obtained through piezoelectric force microscopy measurements, which provide direct and clear evidence for the ferroelectricity in the nanoceramic samples.

Electromechanical properties of tetragonal Pb(In1/2Nb1/2)O3−Pb(Mg1/3Nb2/3)O3−PbTiO3 ferroelectric crystals

The ferroelectric, dielectric, elastic, piezoelectric, and electromechanical properties of tetragonal Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PIN-PMN-PT) crystals were investigated. The single domain piezoelectric coefficients d(33), d(15), and d(31) were found to be 530, 2350, and -200 pCN, respectively, with electromechanical coupling factors k(33), k(15), and k(31) being on the order of 0.84, 0.85, and 0.58. The mechanical quality factor Q for longitudinal mode was found to be >700, with high coercive field (E(c)) being on the order of 10 kVcm. The temperature and dc bias electric-field characteristics of single domain tetragonal PIN-PMN-PT crystals were also investigated. In contrast to [001] oriented domain engineered rhombohedral crystals, tetragonal PIN-PMN-PT crystals exhibited broader temperature usage range and higher thermalelectric field stability, with improved coercive field and mechanical quality factor.

Growth and characterization of Fe-doped Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-0.26PbTiO<sub>3</sub> single crystals

0.3 mol% Fe-doped 0.74Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (PMN-0.26PT) single crystals were grown by a modified Bridgman technique. The structure, dielectric and pyroelectric properties of the Fe-doped crystals were investigated and compared with pure PMN-0.26PT crystals. The investigations showed that small concentrations of Fe substitution increased the coercive field and remnant spontaneous polarization. Two dielectric anomaly peaks were observed under Curie temperature in the dielectric constant versus temperature curve for Fe-doped crystals, which is closer to the room temperature compared with the pure one. The results demonstrate that the domain walls can be pinned by the dopant dipolar defects 2Fe′Ti-Vo, resulting in an increase of coercive field and a decrease of dielectric constant and dielectric loss, which led to the improvement of the detectivity figure of merit (FOM) and kept high voltage responsivity FOM of doped crystals for pyroelectric devices. Such investigation will provide a better understanding of the nature in the complex perovskite materials with high performance.

Surface acoustic wave propagation in Y- and Z-cut 0.67PbMgNbO3–0.33PbTiO3 single crystals

Surface acoustic wave (SAW) propogation in Y-cut and Z-cut relaxor-based 0.67Pb(Mg(13)Nb(23))O(3)-0.33PbTiO(3) (PMN-33%PT) ferroelectric single crystals poled along [001](c) cubic direction has been analyzed theoretically. Characteristic curves were obtained for the phase velocity, electromechanical coupling coefficient and PFA of SAW in Y-cut and Z-cut PMN-33%PT single crystals. It was found that the phase velocity is lower, while the electromechanical coupling coefficient is much higher, than that of traditional piezoelectric materials. The power flow angle (PFA) can be zero in certain directions, which makes this crystal system a promising material for future SAW devices with smaller size and enhanced performance. The directions near 45 degrees and 135 degrees of Y-cut PMN-33%PT crystals are found to be optimum directions for SAW device applications.

Electric-field-induced phase transitions of(1−x)PbMg1/3Nb2/3O3–xPbTiO3 crystals studied by optical methods

The phase transitions of as-grown(1−x)PbMg1/3Nb2/3O3–xPbTiO3 (PMN–xPT) crystals with PTcompositions of x = 0.31 and 0.38 under a dc electric field were observed in a polarization microscope. The opticaltransmissions of the crystals under dc electric fields were measured in the wavelengthregion around their optical absorption edges. The band gaps of the orthorhombic andtetragonal phases under the applied electric field were obtained. By combining both of theoptical methods, the phase transition from the tetragonal to the orthorhombicphase was observed in PMN–0.38PT crystals when the electric field along the[110]cub directionreaches up to 300 V mm−1. Whereas the PMN–0.31PT crystals undergo the pseudo-phase-transition under a dc electric field alongthe [110]cub direction. The pseudo-phase-transition possibly stems from the reorientation and growth ofmicrodomains in PMN–0.31PT crystals.

Investigation of Domain Structure in (001) PMN-x%PT Crystals by Scanning Force Microscope

The domain structures of annealed (001)-oriented <TEX>$Pb(Mg_{1/3}Nb_{2/3})O_3-x%PbTiO_3$</TEX> (PMN-x%PT) crystals for x = 10, 20, 30, 35, and 40 at% were investigated by Polarized Optical Microscopy (POM) and Scanning Force Microscopy (SFM) in the piezoresponse mode. Both Polar Nano-Domains (PND) and long strip-like domains were clearly observed. The results also showed how the domain structure changed between phases with an increasing x in the PMN-x%PT crystals and the domain hierarchy on various length scales ranging from 40 nm to 0.1 mm. Distorted pseudo-cubic phase (x < 20%) consisted of PNDs that did not self-assemble into macro-domain plates. The rhombohedral phase (x = 30%) consisted of PNDs that began to self-assemble into colonies along preferred {110} planes. The monoclinic phase (x = 35%) consisted of miniature polar domains on the nm scale, whereas, the tetragonal phase (x = 40%) consisted of {001} oriented lamella domains on the mm scale that had internal nano-scale heterogeneities, which self-assembled into macro-domain plates oriented along {001} the mm scale.

Tetragonal micro/nanotwins in 0.91Pb(Zn1/3Nb2/3)O3−0.09PbTiO3 revealed by reciprocal space mapping

Reciprocal space mapping (RSM) of the relaxor ferroelectric 0.91Pb(Zn1/3Nb2/3)O3−0.09PbTiO3 (PZN-9%PT) single crystals has been performed by using high-resolution synchrotron x-ray diffraction as a function of temperature. The PZN–9%PT crystal consists of tetragonal micro/nanotwin domains and undergoes a sequence of rhombohedral+tetragonal→tetragonal→cubic phase transformation upon heating. The rhombohedral-to-tetragonal temperature occurs at ≅70 °C. The observed RSM patterns can be explained by the micro/nanotwin structures and their corresponding diffraction patterns.

Canonical molecular dynamics simulations for crystallization of metallic nanodroplets on MgO(100)

The crystallization of Pd, Pt, and Ag nanodroplets in the range of 100--800 atoms (1.5--3 nm diameter) supported on the MgO(100) surface is simulated by canonical molecular dynamics (MD) using tight-binding many-body potentials for the metallic interactions and a potential-energy surface approach fitted to ab initio calculations for the metal-oxide support interaction. The simulations enable to determine the equilibrium supported shapes at finite temperature. These can be compared to the quenched MD simulations or global optimization searches for equilibrium shapes at 0 K. MD simulations at finite temperature after solidification do not display any evidence of a solid-solid transition. The structure is faced-centered cubic with atomic distortions and possible stacking faults. The morphology and epitaxial relation of nanoclusters with their support depend on the size and the nature of the metal: at small sizes (less than 200 atoms), all the metals adopt the (100) epitaxy and Ag clusters keep this epitaxy all over the size range. At 201 atoms (2 nm), Pd clusters are half (111)/half (100) whereas a majority of Pt clusters keeps the (100) epitaxy. At 405 atoms (2.5--3 nm) almost all the Pd clusters change to the (111) epitaxy whereas Pt clusters are half (111)/half (100). The size at which the transition from the (100) to the (111) epitaxy occurs is correlated with the lattice parameter misfit and to the difference in adhesion energy between the two epitaxies.

Low-voltage electron emission from thin [Pb(Mg1/3Nb2/3)O3]0.72 [PbTiO3]0.28 single crystals induced by ferroelectric polarization switching

Electron emission from [Pb(Mg1/3Nb2/3)O3]0.72 [PbTiO3]0.28 (PMN–PT) thin ferroelectric single crystals is reported at ultralow voltages down to 20 V per 400 μm thickness, and for up to 109 switching cycles. The PMN–PT samples were prepared with split gold top electrodes exhibiting a 25 μm wide gap region. Applying a sinusoidal voltage between the two top electrodes and the bottom electrode initiated electron emission from the gap region. The emitted electrons were collected under UHV conditions using two single electron counters arranged under an angle of 90°. Two emission regimes have been identified. Both are attributable to weak electron emission, however, clearly separated by the onset of complete ferroelectric polarization switching. This is also confirmed by recording nanoscale ferroelectric hysteresis loops by means of piezoresponse force microscopy. The emitted electrons are found to have a broad energy distribution with the maximum kinetic energies reaching 110 and 50 eV for applied switching voltages of 140 and 110 V, respectively. Our results confirm that polarization reversal is the governing mechanism behind the electron-emission process in the thin PMN–PT samples. Also, the applied electric field strengths needed to trigger electron emission from the PMN–PT crystals are about 10 times lower compared to most other (ferroelectric) materials reported in the literature.

Ceramic and single-crystal (1 – x)PMN– xPT constitutive behavior under combined stress and electric field loading

Pb(Mg 1/3Nb 2/3)O 3–0.32(PbTiO 3), PMN–0.32PT, single crystals have been characterized under combined stress and electric field loading [McLaughlin EA, Liu T, Lynch CS. Relaxor ferroelectric PMN–32%PT crystals under stress and electric field loading: I-32 mode measurements. Acta Mater 2004;52:3849, McLaughlin EA, Liu T, Lynch CS. Relaxor ferroelectric PMN–32%PT crystals under stress, electric field and temperature loading: II-33-mode measurements. Acta Mater 2005;53:4001] [1–3]. This approach is extended to PMN–0.26PT single crystals to explore the effect of composition on field driven phase transformations and to PMN–0.32PT ceramic specimens to compare with polycrystalline behavior. Electric displacement and strain were measured as a function of combinations of stress and both unipolar and bipolar electric fields. The single-crystal results indicate that compositions further from the morphotropic phase boundary require higher driving forces for field induced phase transformations. Evidence of these transformations is not apparent in the results from the ceramic specimens.

Improved stability for piezoelectric crystals grown in the lead indium niobate–lead magnesium niobate–lead titanate system

Higher coercive fields (EC) and depoling temperatures (TR∕T) were obtained for crystals in the Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIN–PMN–PT) ternary system. Data are given for a crystal boule with starting composition 0.24PIN-0.44PMN-0.32PT, and with chemical distributions along the growth direction. The dielectric, piezoelectric, and elastic properties were determined. Similar to binary PMN–PT, ternary PIN–PMN–PT crystals have outstanding piezoelectric properties (e.g., d33∼900–1900pm∕V, k33∼0.83–0.92). In addition, PIN stabilizes piezoelectric performance by doubling EC (∼6kV∕cm) and increasing TR∕T by ∼20°C. These improvements are advantageous for acoustic transducers used in high-drive applications.

Electromechanical coupling coefficient of 0.70Pb(Mg1∕3Nb2∕3)O3–0.30PbTiO3 single crystal resonator with arbitrary aspect ratio

Based on mode coupling theory and the fundamental energy ratio definition of the electromechanical coupling coefficient, a unified formula has been derived to calculate the effective electromechanical coupling coefficient keff of 0.70Pb(Mg1∕3Nb2∕3)O3–0.30PbTiO3 (PMN-30%PT) ferroelectric single crystal cylindrical resonator with arbitrary aspect ratio. The keff dependence on resonator aspect ratio of PMN-30%PT crystal shows similar characteristics as that of the conventional piezoelectric ceramics Pb(ZrxTi1−x)O3 (PZT). However, compared to PZT-5 ceramics, PMN-30%PT single crystal has a smaller aspect ratio where the keff changes dramatically and there is also a stronger coupling between thickness and radial modes causing much larger mode splitting.

Structure and properties of multiferroic (1 − x)BiFeO3–xPbTiO3 single crystals

Single crystals of the multiferroic (1 − x)BiFeO3–xPbTiO3 (BF–PT) solid solution with a nominal morphotropic phase boundary (MPB) composition were grown from flux. Structural characterization by x-ray diffraction shows the simultaneous existence of a tetragonal, an orthorhombic, and a rhombohedral perovskite phase in the crystals. A high ferroelectric Curie point of 660 °C was found in the BF–PT crystals by dielectric measurements. The variation of the magnetic moment as a function of temperature of the BF–PT crystals measured under zero field cooling mode reveals three anomalies with the highest one around 440 K, corresponding to the antiferromagnetic ordering temperatures of the rhombohedral, orthorhombic, and tetragonal phases, respectively. These results demonstrate the intrinsic relations between the MPB phase components and the macroscopic ferroic properties.

Correlation between non-180° domain structures in (1−x)PbA1∕3Nb2∕3O3−xPbTiO3 single crystals (A=Mg or Zn) under an applied [001] electric field

This work is devoted to the study of heterophase states in (1−x)PbA1∕3Nb2∕3O3−xPbTiO3 or PAN−xPT (A=Mg or Zn) single crystals under an electric field ‖E‖[001]. The possibility of elastically matched phases in the transformational sequences of Pm3m→P4mm→Cm, Pm3m→Cm, and P4mm→Cm are considered with regards to non-180° domains and changes in lattice parameters. Systems of diagrams linking domain types with interfaces between coexisting polydomain phases in PMN–0.28PT and PZN–0.045PT crystals are given. An important role of an intermediate P4mm phase in achieving stress accommodation has been identified by analysis of lattice parameters of PMN–0.28PT, and the elastic compatibility conditions between non-180° domain structures in the P4mm and Cm phases have been determined for various heterophase states. Two scenarios of changes in the lattice parameter aT in the P4mm phase of PMN–0.28PT have first been discussed to reveal possibilities of stress accommodation in heterophase states. It has been shown that the correlation between domain structures in different heterophase states of studied crystals stems from coordinated unit-cell behavior under ‖E‖[001].

Characterization of All the Elastic, Piezoelectric, and Dielectric Constants of Tetragonal Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystals have a tetragonal 4 mm symmetry. In this paper, the elastic, piezoelectric, and dielectric constants of PMN–PT single crystals were measured by the resonance method. A total of eleven independent material constants were measured including six elastic compliance constants at a constant electric field, two dielectric constants at constant stress, and three piezoelectric constants d. Four crystal sample sets of different geometries were prepared in order to measure the length–thickness extensional, thickness extensional, length extensional and thickness shear modes of vibrations, respectively. The experimental impedance spectrum of the PMN–PT crystals was compared with a numerical impedance spectrum calculated with the measured material constants. Good agreement between the two spectra confirmed the validity of the characterization method. In addition, the piezoelectric constant d33, which was determined by the resonance method, was also compared with that measured by a commercial d33 meter. This further confirmed the validity of the resonance measurements.

Acoustic Emission Study of PZN-7%PT Crystals

Phase transitions in PbZn 1/3 Nb 2/3 O 3 -7%PbTiO 3 (PZN-7%PT) relaxor ferroelectric crystals have been investigated by the acoustic emission (AE) method. Two types of transitions have been detected: (i) associated with the thermally induced (on cooling) formation of intrinsic polar nanoregions (PNRs) and (ii) related to the electric-field-induced macroscopic phase transitions. An AE signal found near 740 K corresponds to the Burns temperature, below which the PNRs begin to form. Further cooling reveals an AE signal at 500 K, which is ascribed to the shift of PNRs along their polar direction relative to the surrounding non-polar matrix in the framework of the “phase-shifted condensed soft mode” model. Monitoring of the AE response of PZN-7%PT crystals under an increasing [001] dc electric field has allowed a unique in situ observation of a sequence of phase transitions, from the zero-field rhombohedral via M A monoclinic (∼ 3 kV/cm) and M C monoclinic (∼ 16 kV/cm) to the tetragonal (∼ 19 kV/cm) phase, respectively. It is shown that AE is a very sensitive method for detecting both the PNRs kinetics and low distortion phase transitions in relaxor ferroelectrics.

Orthorhombic and monoclinic ferroelectric phases investigated by Raman spectroscopy in PZN-4.5%PT and PZN-9%PT crystals

Polarized Raman spectra measurements have been performed on orientated single crystals of Pb[(Zn 1/3Nb 2/3) 0.955Ti 0.045]O 3 (PZN-4.5%PT) and Pb[(Zn 1/3Nb 2/3) 0.91Ti 0.09]O 3 (PZN-9%PT) poled by an electric field along the [ 1 ̄ 01 ] pseudo-cubic direction in order to determine the nature of the induced ferroelectric phases. Under field-cooled (FC) conditions the ferrolectric phase transition sequence, tetragonal–orthorhombic–rhombohedral, was observed in PZN-4.5%PT. Comparison between the phase transitions induced in PZN-9%PT and PZN-4.5%PT crystals in FC shows that the low- temperature ferroelectric phase in PZN-9%PT cannot be orthorhombic and it can be attributed to the monoclinic phase. The characteristic temperatures found by Raman spectroscopy correspond to those obtained by dielectric measurements and by X-ray diffraction reported previously.

Fatigue induced effects on bipolar strain loops in PZN-PT piezoelectric single crystals

Polarization and bipolar strain hysteresis (P-E and S-E) measurements were performed simultaneously during fatigue tests performed under ac fields with a triangular wave form. Rhombohedral (1-x)Pb(Zn1/3Nb2/3)O3−xPbTiO3 (PZN-PT) piezo/ferroelectric single crystals demonstrate a wide variety of anisotropic behavior under bipolar electrical switching. Specifically, PZN-4.5 PT crystals demonstrate exceptional polarization switching fatigue resistance along [001]C (-c; pseudocubic), as opposed to normal fatigue in [111]C directions. This system provides an excellent opportunity to study fatigue induced effects in [111]C orientation in comparison with [001]C. Studies in bulk ferroelectric ceramics have reported fatigue-associated strain hysteresis asymmetry. In this study, the evolution of bipolar strain loops was studied in both “fatiguing” [111]C and “fatigue-free” [001]C orientations. It was found that [111]C oriented PZN-4.5 PT crystals show the onset of a strain-field asymmetry displayed by shortage of one wing of the butterfly, which becomes more evident as cycling continues. In contrast, [001]C crystals show symmetrical strain-field curves throughout cycling. S-E hysteresis data obtained from different points in a fatigued crystal by gently moving it between the consecutive measurements show that the shorter wing switches side indicating the local character of fatigue. In comparison to the findings in polycrystalline ceramics this observation in a single crystal ferroelectric will be helpful for a better understanding of fatigue and related effects. Rejuvenation studies in fatigued crystals are also reported in this paper.

Selection and Discovery of Polymorphs of Platinum Complexes Facilitated by Polymer-Induced Heteronucleation

Polymer-induced heteronucleation was utilized for the selective crystallization of the color polymorphic platinum complexes Pt(bpy)Cl2 and Pt(phen)Cl2. Crystal structures of two polymorphs of Pt(phen)Cl2 were determined and reveal that, as in the case of Pt(bpy)Cl2, this compound has one form with Pt...Pt interactions (orange crystals) and another lacking these contacts (yellow crystals). Free energy measurements reveal that the polymorphs of Pt(bpy)Cl2 and Pt(phen)Cl2 without Pt...Pt interactions are more stable in both cases by 0.67(2) and 0.53(1) kJ/mol, respectively, and this finding is consistent with the principle of close packing. Furthermore, a search of the Cambridge Structural Database reveals that, for polymorphic platinum complexes, shorter intermolecular Pt...Pt interactions generally result in less dense structures.

Properties of Single Domain Pb(Zn1/3Nb2/3)O3–(6–7)%PbTiO3 Single Crystal

A complete set of elastic, piezoelectric and dielectric properties of a [111]-poled single-domain Pb(Zn1/3Nb2/3)O3–(6–7)%PbTiO3, or PZN–(6–7)%PT, single crystal have been determined by means of a combination of resonance and quasi-static measurement techniques. The present work shows that the d15 value determined by the resonance measurement technique using a length-shear sample and that measured by quasi-static measurement technique are comparable, suggesting that the length-shear resonance behavior is valid for a crystal of 3 m symmetry provided that the length-to-thickness ratio is sufficiently large, for example, >10. The single-domain PZN–(6–7)%PT crystal exhibits very high d15 and d22 values, namely, 6000 and -1280 pC/N, respectively.