James M. Powers

Importance of random fields on the properties and ferroelectric phase stability of 〈001〉 oriented 0.7 Pb(Mg1/3Nb2/3)O3–0.3 PbTiO3 crystals

Temperature dependent dielectric constant measurements have been performed on 〈001〉 oriented 0.7 Pb(Mg1/3Nb2/3)O3–0.3 PbTiO3 crystals. These investigations have revealed an irreversible secondary transformation between a normal ferroelectric state and a relaxor ferroelectric state with increasing temperature. The results demonstrate that the anisotropy of the high performance piezocrystal state is only metastably locked in under application of field. Clearly, local random fields play a crucial role upon the ferroelectric phase stability and properties of 〈001〉 oriented piezocrystals.

Effect of uniaxial stress on the large-signal electromechanical properties of electrostrictive and piezoelectric lead magnesium niobate lead titanate ceramics

The electromechanical performance characteristics of electrostrictive 0.9 Pb(Mg1/3Nb2/3)O3–0.1 PbTiO3 and piezoelectric 0.7 Pb(Mg1/3Nb2/3)O3–0.3 PbTiO3 ceramics have been investigated under uniaxial stress (σ). The results demonstrate that the large-signal electromechanical properties of electrostrictive ceramics are decreased with increasing σ, whereas those of the piezoelectric are increased but accompanied by significantly increased hysteretic losses.

Stress dependence of the electromechanical properties of 〈001〉-oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals: Performance advantages and limitations

The electromechanical properties of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 〈001〉-oriented crystals have been investigated under unaxial stress (σ). The results demonstrate enhanced piezoelectric coefficients and electroacoustic power densities with increasing σ. However, these increases are accompanied by significant increases in hysteretic losses. The results also demonstrate that the electromechanical coupling coefficient (∼0.92) is relatively independent of σ between 0 and 6×107 N/m2. Future transducer designs can rely on piezocrystals offering a k33 of 0.92, 10 dB more power, and low losses under operational conditions of σ<107 N/m2 and 5<T<40 °C.The electromechanical properties of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 〈001〉-oriented crystals have been investigated under unaxial stress (σ). The results demonstrate enhanced piezoelectric coefficients and electroacoustic power densities with increasing σ. However, these increases are accompanied by significant increases in hysteretic losses. The results also demonstrate that the electromechanical coupling coefficient (∼0.92) is relatively independent of σ between 0 and 6×107 N/m2. Future transducer designs can rely on piezocrystals offering a k33 of 0.92, 10 dB more power, and low losses under operational conditions of σ<107 N/m2 and 5<T<40 °C.

Single-crystal lead magnesium niobate-lead titanate (PMN/PT) as a broadband high power transduction material

Two experimental underwater acoustic projectors, a tonpilz array, and a cylindrical line array, were built with single crystal, lead magnesium niobate/lead titanate, a piezoelectric transduction material possessing a large electromechanical coupling factor (k33 = 0.9). The mechanical quality factor, Q(m), and the effective coupling factor, k(eff), determine the frequency band over which high power can be transmitted; k(eff) cannot be greater than the piezoelectric material value, and so a high material coupling factor is a requisite for broadband operation. Stansfields bandwidth criteria are used to calculate the optimum Q(m) value, Q(opt) approximately 1.2 (1-k(eff)2 1/2/k(eff). The results for the tonpilz projector exhibited k(eff) = 0.730, Q(m) = 1.17 (very near optimal), and a fractional bandwidth of 0.93. For the cylindrical transducer array, k(eff) = 0.867, Q(m) = 0.91 (larger than the optimum value, 0.7), and the bandwidth was 1.16. Although the measured bandwidths were less than optimal, they were accurately predicted by the theory, despite the highly simplified nature of the Van Dyke equivalent circuit, on which the theory is based.

Enhancement of electromechanical coupling coefficient and acoustic power density in conventional “Hard” Pb(Zr1−xTix)O3 ceramics by application of uniaxial stress

Investigations of the polarization versus electric field (P-E) and strain versus electric field (e-E) responses for “hard” Pb(Zr1−xTix)O3 piezoelectric ceramics have been performed under various uniaxial stresses (σ) and ac electrical drive fields. Investigations revealed a significant decrease in the remanent polarization of specimens with increasing σ. Subsequent calculations of the longitudinal electromechanical coupling coefficient (k33) and acoustic power density revealed significant enhancements with increasing σ.

Ferroelastic switching and elastic nonlinearity in 〈001〉-oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Zn1/3Nb2/3)O3–PbTiO3 crystals

The strain versus electric field (e−E) and strain versus stress (e−σ) response characteristics of 〈001〉-oriented crystals of Pb(BI1/3BII2/3)O3–PbTiO3 have been investigated. Under zero field, a ferroelastic switching has been observed under moderate uniaxial prestress levels. The magnitude of the elastic strain switched was ∼0.4%. In addition, an elastic softening was observed during switching, where the elastic constant decreased from ∼1010 to ∼3×109 N/m2. At higher stresses, the elastic constant stiffened to ∼5×1010 N/m2, which upon application of dc electrical bias softened to ∼1010 N/m2. The importance of ferroelastic switching and elastic nonlinearity is discussed.

Characterization of PMN‐PT‐La for use in high‐power electrostrictive projectors

There is increasing interest in relaxor ferroelectrics such as PMN‐PT‐La,Ba (lead magnesium niobate‐lead titanate doped with lanthanum or barium) for use as high‐power transducer driver materials in lightweight projector arrays. These electrostrictive materials have been shown to have induced strains an order of magnitude greater than PZT at modest electric fields. The drawback, however, is that the response of the material is dependent on frequency, prestress, temperature, and ac drive and dc bias fields. To date no measurements have been made of all these relationships for 33‐mode vibration applications. In this study, using various mechanical prestresses, quasistatic room temperature measurements were made of the piezoelectric constant, d33, of the relative permittivity, e33T/e0, and of the short‐circuit Young’s modulus, Y33E for PMN‐PT‐La (TRS Ceramics, Inc., 0.90 / 0.10 /1%, 31 March 1995). Electric fields of up to 2 MV/m were applied to samples (2×2×10 mm that were prestressed from 0 to 12 ksi (83 M...

BIASED LEAD ZIRCONATE TITANATE AS A HIGH-POWER TRANSDUCTION MATERIAL

High‐power, underwater transducers using polarized piezoelectric ceramic material are usually limited in drive amplitude so that depolarization does not occur, but application of a dc bias field in the polarization direction allows the use of higher ac drive fields. To demonstrate the feasibility of a biased operation as a means of achieving higher power, a thin‐walled, spherical‐shell transducer was constructed of Channel 5800 and tested in NUWC’s Acoustic Pressure Tank Facility. The transducer was successfully driven to 33 V/mil (1.3 MV/m) rms with an accompanying bias field of 31 V/mil (1.2 MV/m) and a hydrostatic pressure of 1400 psig (9.65 MPa). The source level was 206 dB//mPa‐m at 61 kHz, corresponding to a 10‐dB improvement over the usual Navy standard unbiased drive limit of 10 V/mil (0.4 MV/m) rms. [Work supported by ONR.]

Omnidirectional ultrasonic microprobe hydrophone

An omnidirectional ultrasonic microprobe hydrophone is disclosed. Applicans include underwater mine detection, explosive shock testing, high wave number measurements, medical imaging, and therapeutic systems. The apparatus includes at least two lead zirconate titanate (PZT) pressure sensing elements having a plurality of columnar voids formed therein. The pressure sensing elements are deposited on a metallic or nonmetallic substrate which provides mechanical support for the microprobe hydrophone. Electrical connection to the pressure sensing elements is made by deposition of conductors and insulators on the substrate material. Wire bonds are used to attach wire leads for connection to a supporting structure containing a preamplifier. Line arrays and planar arrays of microprobe hydrophone elements are also disclosed.

Property measurements on piezoelectric single crystals and the implications for transducer design

Piezoelectric single crystals of lead magnesium niobate in solid solution with lead titanate have generated great interest in the Navy sonar community because of the potential they offer for enhanced transducer performance. Two material properties, in particular, make the piezoelectric single crystals unique; their high 33-mode coupling factor and their low short circuit Youngs modulus. Measurements of the large signal electromechanical and mechanical properties on single crystal samples are presented in this paper. These measurements elucidate the behavior of piezoelectric single crystals, including the effect of bias field on the Youngs modulus. The ramifications of the measured material properties on transducer design are also discussed.