Magnesium Niobate-lead Titanate Single Crystals Research Articles

Dense ferroelectric-ferroelastic domain structures in rhombohedral PMN-28PT single crystals

We have studied a dense domain structure (DDS) appearing during polarization reversal in rhombohedral (111)-cut lead magnesium niobate-lead titanate single crystals. The complicated shape of the switching current was explained by means of non-uniform motion of the boundary between the DDS and c-domains using comparative analysis of the optical current and kinetic map. 2D-vector piezoresponse force microscopy revealed that DDS represented needle-like a-domains inside the a-domains with different vertical orientations of spontaneous polarization.

Material Measures of Electrocaloric Cooling Power in Perovskite Ferroelectrics

AbstractMany ferroelectric materials that can serve as refrigerants in electrocaloric cooling devices have been identified. To compare them, material measures of cooling power are useful. The electrocaloric performance characteristics of ferroelectric materials are determined to a large degree by the nature of the paraelectric to ferroelectric phase change, which influences the magnitude of the electrocaloric effect and the variation with temperature of the thermal conductivity and heat capacity. Here, those properties are compared for three promising ferroelectric materials. The materials chosen for study have differing phase change characteristics ranging from first‐order to diffuse/relaxor‐like behavior, and include barium titanate and lead magnesium niobate—lead titanate single crystals and polycrystalline barium zirconate‐titanate ceramics. Using measured thermophysical property data, and a simple model based on the Newtonian cooling of a thin plate, the dependences of the material cooling power on the dimensionless temperature, characteristic distance, and holding time for heat transfer are determined. Relationships existing between material cooling power and the nature of the phase transition, thermophysical properties, and the electrocaloric behavior are illustrated. Although device‐level factors, such as thermal resistances at electrode interfaces are ignored, the results suggest a simple basis of comparison for electrocaloric materials.

Investigation of domain structure evolution during zero-field temperature treatment in 0.67PMN-0.33PT single crystals

ABSTRACTThe temperature depolarization process has been studied in [001]-cut lead magnesium niobate-lead titanate single crystals with 33% lead titanate content by in situ visualization of as-grown domain structure evolution during zero-field heating and subsequent cooling. The phase transitions have been revealed during heat treatment. It has been shown by piezoresponse force microscopy and scanning electron microscopy that heat treatment leads to decay of maze-type as-grown domain structure into array of irregular domains with average diameter about 300 nm. Shallow etching of the surface during mechanochemical polishing has allowed keeping the surface relief corresponding to as-grown domain pattern.

Polarization reversal and domain kinetics in PMN-30PT single crystals

ABSTRACTPolarization reversal process has been studied in [001]-cut lead magnesium niobate-lead titanate single crystals with 30% lead titanate by in situ visualization of domain kinetics and switching current analysis. It has been shown by high-resolution methods that the sample poling leads to partial decay of as-grown domain structure and decrease of the domain width down to 200 nm. Analysis of the switching current by modified Kolmogorov-Avrami approach has shown that the field dependence of the characteristic time follows activation law with activation field value 1040±50 V/mm. In situ visualization has allowed revealing the main stages of domain structure evolution.

PMN-PT single crystal for endoscopic ultrasound 2D array application

Based on lead magnesium niobate-lead titanate single crystal, a 24 × 24 row-column addressing endoscopic two-dimensional array has been successfully fabricated using novel flanged electrodes and “semi-kerf” technologies. Each row/column array element was measured to have an electromechanical coupling coefficient of 0.81, a center frequency of 5MHz, and a fractional bandwidth of approximately 88% at −6 dB. Of particular significance was that the lead magnesium niobate-lead titanate element exhibits much higher sensitivity compared with lead zirconate titanate-based 2D arrays with similar operational frequency and element area. According to the Field II simulated results, although the obtained beamwidth at −6 dB was a little inferior to that of the fully sampled 24 × 24 two-dimensional array, it is believed that the beamwidth can be improved by appropriately increasing the element number. These results demonstrated that the lead magnesium niobate-lead titanate single-crystal 2D array is a promising candidate for real-time three-dimensional endoscopic ultrasound imaging.

Scandium modified lead magnesium niobate-lead titanate single crystals for high temperature and high power applications

Within the morphotropic phase boundary region, 0.39PSN-0.13PMN-0.48PT crystals exhibit excellent properties. The dielectric response of poled 〈001〉-oriented 0.39PSN-0.13PMN-0.48PT crystal plates displays non-relaxor behavior with Curie and depolarization temperatures of about 230°C and 199°C, respectively, exhibiting high temperature stability of the ferroelectric phase. The saturated polarization-electric field loop of the same plate manifests the switching of domains, with the coercive field of approximately 5.6kV/cm, indicating stable piezoelectric properties. The out of plane and in plane domain configurations exhibit obvious domain walls. The typical butterfly strain-electric field curve presents a large peak to peak strain value of about 0.59%. The piezoelectric constant is calculated to be about 1670pC/N from the unipolar stain-electric field curve.

Composition dependence of field induced phase transformations in [0 1 1]C PIN–PMN–PT relaxor ferroelectric single crystals with d322 piezoelectric mode

Relaxor ferroelectric single crystals are used in sonar, medical ultrasound, accelerometers and energy-harvesting applications due to their large electromechanical coupling. In this work, the compositional dependence of the electromechanical properties of [011]C cut relaxor ferroelectric lead indium niobate–lead magnesium niobate–lead titanate single crystals, xPb(In1/2Nb1/2)O3–(1-x-y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 (PIN–PMN–PT) was determined. The effect of increasing the concentration of lead indium niobate (xPIN) and increasing the concentration of lead titanate (yPT) on compositions near the morphotropic phase boundary was explored. Specimens were subjected to combined electrical, mechanical and thermal loading. The electric field induced changes of polarization and strain were measured at a series of preload stresses and the stress induced polarization and strain changes were measured at a series of bias electric fields. This was repeated at several temperatures. Evidence of a phase transformation from ferroelectric rhombohedral to ferroelectric orthorhombic was observed in the form of jumps in strain and electric displacement at critical field levels. The linear piezoelectric constant, dielectric permittivity, elastic compliance, thermal expansion, pyroelectric coefficient and rate of change of the material properties with temperature were determined including a scalar measure of electromechanical work indicating the start of the field induced phase transformation.

Enhanced magnetoelectric effect in a stress-biased lead magnesium niobate-lead titanate single crystal/Terfenol-D alloy magnetoelectric sensor

A stress-biased magnetoelectric sensor with a built-in permanent magnet has been fabricated using piezoelectric lead magnesium niobate-lead titanate single crystal and magnetostrictive Terfenol-D alloy. The resonance characteristics and magnetoelectric performance of the sensor have been evaluated under different stress-biased conditions. The resonance of the sensor shifts to higher frequency with increasing preloading stress. Due to the piezoelectric and magnetostrictive enhancements under preload, the device exhibits a giant magnetoelectric voltage coefficient of 0.22 V/Oe at a preloading stress of 2.5 MPa. This compact device has the potential to be used as a standalone sensor without requiring external power input.

High-pressure vertical Bridgman growth of lead magnesium niobate–lead titanate single crystal

A modified high-pressure vertical Bridgman (HPVB) method has been used to grow single crystals of lead magnesium niobate–lead titanate (PMN–PT) using self-seeding. The starting charge was prepared close to stoichiometric composition of (1− x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3, ranging from x=0.29 to x=0.32. The ingots grown had a top diameter of ∼114 mm and weighing ∼1.9 kg with a volume of ∼230 cc. Standard form off-the-shelf platinum crucibles from vendors with a wall thickness ∼0.34±0.01 mm were used. The thinner platinum helped to attain a larger radial thermal gradient as well as enhancing the cost effectiveness of the process by reducing usage of precious metals. An oxygen partial pressure of 8000–10 000 ppm was used and controlled during the entire growth process. Self-seeding technique was used in order to attempt to grow large diameter single crystals of PMN–PT. The composition variation in the ingot is dependent on the growth rate, thermal gradients and oxygen partial pressure. The segregation coefficient of Ti was 0.86±0.008 for the starting composition of x=0.32.

Derivation of Piezoelectric Losses from Admittance Spectra

High power density piezoelectrics are required to miniaturize devices such as ultrasonic motors, transformers, and sound projectors. The power density is limited by the heat generation in piezoelectrics, therefore, clarification of the loss mechanisms is necessary. This paper provides a methodology to determine the electromechanical losses, i.e., dielectric, elastic and piezoelectric loss factors in piezoelectrics by means of a detailed analysis of the admittance/impedance spectra. This method was applied to determine the piezoelectric losses for lead zirconate titanate ceramics and lead magnesium niobate-lead titanate single crystals. The analytical solution provides a new method for obtaining the piezoelectric loss factor, which is usually neglected in practice by transducer designers. Finite element simulation demonstrated the importance of piezoelectric losses to yield a more accurate fitting to the experimental data. A phenomenological model based on two phase-shifts and the Devonshire theory of a polarizable–deformable insulator is developed to interpret the experimentally observed magnitudes of the mechanical quality factor at resonance and anti-resonance.

Central peak and acoustic anomalies of the relaxor ferroelectric lead magnesium niobate-lead titanate single crystal studied by the micro-Brillouin scattering

Quasielastic central peak and acoustic anomalies in a [001] lead magnesium niobate-lead titanate single crystal have been investigated by the high-resolution micro-Brillouin scattering. Two acoustic anomalies were observed at temperatures, TC-T∼415K and TT-R∼348K. The damping showed a significant dispersion at T∼550K, associated with the enhanced dynamics of local strain fields created by the polar microregions. The temperature evolution of the quasielastic central peak exhibited anomalies in the overall intensity and relaxation time that were associated with the line shape interferences of the central peak and the acoustic mode.

High transition temperature lead magnesium niobate–lead zirconate titanate single crystals

Recently developed relaxor lead magnesium niobate–ferroelectric lead zirconate titanate single crystals exhibit large length extensional k33 coupling, improved thermal stability, and a higher coercive field compared to morphotropic lead magnesium niobate–lead titanate single crystals. Experimental results and implications for sound projectors are presented and discussed in terms of the morphotropic phase boundary slope and width. Spontaneous polarizations derived from the calculated atom shifts in both crystals compared favorably with experimental values.

Ferroelectric lead magnesium niobate–lead titanate single crystals for ultrasonic hydrophone applications

Ferroelectric lead magnesium niobate–lead titanate (PMN–PT) single crystals with a composition around the rhombohedral–tetragonal morphotropic phase boundary (65 mol% of PMN) were used to fabricate single-element needle-type hydrophones for measuring the spatial and temporal characteristics of medical ultrasonic transducers. PMN–PT single crystal was grown by a modified Bridgman method. Discs (0.5 mm thick) with normal along the 〈0 0 1〉 direction were cut and then poled by a dc field in the thickness direction. The single crystal has a high relative permittivity ( ε r∼4000) making it appropriate for small area hydrophone applications. Single-element needle-type hydrophones with this material as the sensing element have been fabricated and characterized. The hydrophones have flat frequency response and good receiving sensitivity over certain frequency range in the megahertz region.

Growth and observation of domain structure of Lead Magnesium Niobate–Lead Titanate Single Crystals

(1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMNT) single crystals were grown by the vertical Bridgman method, and the spatial domain configurations in the rhombohedral and tetragonal crystals were observed using a polarizing microscope, SEM, and SFM in piezo response mode. In the rhombohedral crystals, both regular tire-track patterns and irregular fingerprint patterns were observed on the as-grown crystal plates. The tire-track patterns were composed of {100} and {110} domain walls. The irregular fingerprint patterns were antiparallel domains. In the tetragonal crystals, 3 different types of etching areas were observed. These patterns consisted of 180° domains and 90° {110} domain boundary.

Brillouin scattering investigations of lead magnesium niobate–lead titanate single crystal

Lead magnesium niobate–lead titanate (PMN–PT) [0 0 1] single crystal of morphotropic phase boundary (MPB) composition; have been studied by 90A Brillouin scattering technique. Two phase transition anomalies were observed in the temperature dependences of Brillouin frequency shift ( ν) and full-width at half-maximum of the LA and TA modes at T∼336 and ∼415 K associated with symmetry changes from R3 m to P4 mm and P4 mm to Pm 3 ̄ m, respectively. The observed spectra showed strong polarization dependence in cubic and tetragonal phases, whereas in rhombohedral phase both the VV- and VH-scattering spectra were similar. This effect was attributed to the rotation of spontaneous polarization due to change of symmetry from P4 mm to R3 m.

Segregation during the vertical Bridgman growth of lead magnesium niobate–lead titanate single crystals

Transparent, high-quality lead magnesium niobate–lead titanate, (1− x)PbMg 1/3Nb 2/3O 3– xPbTiO 3, or PMNT, crystals were grown using the vertical Bridgman method. Crystals grown from 35% PT ( x=0.35) and 32% PT ( x=0.32) melts were found to vary in composition along the axial direction (from 30% to 72% PT along the growth direction). Crystals grown from 10% PT melts were found to be uniform in composition. Effective segregation coefficients were determined. All crystals examined had uniform radial composition profiles, indicating a flat growth interface. Dielectric measurements were performed on (0 0 1) oriented samples cut from a crystal grown from a 35% PT melt. Powder X-ray diffraction analysis revealed the presence of a two-phase region (tetragonal and rhombohedral) between 31% PT and 36% PT. Poling was performed on (0 0 1) samples of composition 32% PT. Upon poling, as-grown, cloudy crystals became optically transparent, and observations under crossed polarizers showed the formation of large single domain regions. Analysis of 32% PT samples showed a transition from two phases (rhombohedral and tetragonal) in the as-grown sample to single phase (rhombohedral) after poling. The high-temperature phase diagram for PMNT was estimated using a combination of differential thermal analysis and compositional data from growth experiments.