Ahmed Amin

Study of phase transitions in ternary lead indium niobate-lead magnesium niobate-lead titanate relaxor ferroelectric morphotropic single crystals

In this work we report on the elastic hysteretic behavior observed in ferroelectric lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) relaxor single crystals under conditions of cooperative stress, temperature, and electric field. Room temperature elastic response displays strong and sharp discontinuity associated with stress induced phase transition. Quasistatic elastic response and ultrasonic wave propagation measurements demonstrated that this strain discontinuity in PIN-PMN-PT single crystal is associated with a ferroelectric rhombohedral (FR)—ferroelectric orthorhombic (FO) phase transition. The temperature dependent elastic response and transition strain were modeled by Devonshire theory. The crystal instability under compression is significantly improved by application of a dc bias electric field.

Mechanical and thermal transitions in morphotropic PZN-PT and PMN-PT single crystals and their implication for sound projectors

Isothermal compression experiments on multidomain [001] oriented and poled ferroelectric rhombohedral PZN-0.07PT and PMN-0.30PT single crystals revealed elastic instabilities corresponding to zero field ferroelectric-ferroelectric phase transition under mechanical compression. The application of an appropriate dc bias field doubled the stability range of the ferroelectric rhombohedral state under uniaxial compression for both crystals and maintained a linear elastic response. Youngs modulus as derived from the quasistatic, zero field stress-strain linear response agreed well with that derived from small signal resonance for the ferroelectric rhombohedral FR state of both PZN-PT and PMN-PT. Elastic compliances S33 E as determined from high temperature resonance revealed a monotonically decreasing Youngs modulus as a function of temperature in the ferroelectric rhombohedral state with a sudden stiffening near the ferroelectric rhombohedral (FR)-ferroelectric tetragonal (FT) transition. The reversible ferroelectric-ferroelectric transition of morphotropic PZN-PT and PMN-PT single crystals as accessed by mechanical compression is discussed in terms of strain calculations from Devonshires theory, domain unfolding, and morphotropic phase boundary shift with mechanical stress. The mechanically-induced and thermally-induced ferroelectric-ferroelectric transition trajectories are discussed in terms of the Devonshire theory. Implications of these observations for sound projectors are discussed. A single crystal tonpilz projector fabricated into a 16-element array and a segmented cylinder transducer demonstrated the outstanding capabilities of single crystals to achieve compact, broadband, and high-source level projectors when compared to conventional lead zirconate-titanate PZT8 projectors.

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.

Large strain transduction utilizing phase transition in relaxor-ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

In this work, we present experimental evidence that under relatively low level drive (<0.1 MV/m) the large strain (∼0.5%) associated with ferroelectric rhombohedral FR-ferroelectric orthorhombic FO phase transition in domain engineered relaxor–ferroelectric single crystals under compressive stress and bias electric field can be captured. We have demonstrated this in mechanically confined ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals poised at the rhombohedral side of the morphotropic phase boundary. Experimental strain-field results, methods of mechanical confinement and drive, and a low frequency, compact, high source level sound projector design are presented. Transducers that operate on a large strain principle as a design rule will benefit from this development.

dc field effect on stability of piezoelectric PZN-0.06PT single crystals under compressive stress

A reversible elastic instability was observed in PZN-0.06PT high coupling single crystals when subjected to uniaxial compressions similar to those used in sound projectors. The strain magnitude at the onset of the instability supported a free energy prediction of a ferroelectric rhombohedral (FR)-ferroelectric orthorhombic (FO) phase transition. The thermal response of the normalized phase transition strain is in a good agreement with model calculation. A dc bias field drastically enhanced the crystal stability under compression. dc bias and compressive stress levels that are required for their stable operation in sound projectors have been deduced and will be presented.

Elasticity of high coupling relaxor-ferroelectric lead zinc niobate-lead titanate crystals

The elastic response of a [001]-oriented and -poled ferroelectric rhombohedral lead zinc niobate-lead titanate single crystal close to the morphotropic phase region is examined under thermal, electrical, and mechanical boundaries similar to those used in sound projectors. Resonance measurements yielded a monotonically decreasing Young’s modulus as a function of temperature in the ferroelectric rhombohedral state with a sudden stiffening near the ferroelectric rhombohedral (FR)-ferroelectric tetragonal (FT) transition. The quasistatic, zero-field stress-strain response revealed a FR instability under uniaxial compression. A dc bias field stabilized the FR state under compressive stress. Young’s modulus derived from the linear elastic response below instability agrees well with resonance data for FR. A larger modulus than expected for FT was observed above instabilities. The elastic response is analyzed in terms of ferroelectric-ferroelectric transitions as predicted by a high-order Devonshire theory. Impli...

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.

Trapped metastable phases in Pb(Zn1/3Nb2/3)O3–(8–9)%PbTiO3 single-crystal wafers

In addition to locally stressed rhombohedral phase, evidence for trapped metastable phases in (001)-cut single-crystal wafers of Pb(Zn1/3Nb2/3)O3–(8–9)%PbTiO3 has been obtained by means of the x-ray diffraction technique. The rhombohedral phase is stressed predominantly in compression in the plane of the wafer, both in unpoled and poled conditions, giving rise to the broad shoulder at the lower 2θ end of the rhombohedral peak. Trapped tetragonal phase, with its c axis lying both in the plane and perpendicular to the plane of the wafer, can also be detected in as-sliced, unpoled wafers. Upon poling along the [001] thickness direction, the tetragonal phase with its c axis lying in the plane of the wafer is transformed readily to the rhombohedral phase. In contrast, a minute amount of tetragonal phase with its c axis perpendicular to the plane of the wafer can be stabilized by the stressed rhombohedral matrix in poled state. At sufficiently high poling fields (i.e., ⩾1.2 kV/mm), a trapped pseudomonoclinic ph...

Transitions in Morphotropic PMN-PT Single Crystals

Single crystals in the relaxor-ferroelectric lead magnesium niobate (PMN)-lead titanate (PT) and lead zinc niobate (PZN)-lead titanate (PT) systems provide a significant advantage for detecting and classifying objects in littoral waters. Their extremely large electromechanical coupling factor (k 33 > 0.90) and piezoelectric coefficient (d 33 > 1000 pC/N) offer both broadband and high acoustic source level capabilities. Two different transition pathways can be accessed in a morphotropic PMN-0.30PT composition. Resonance experiments on a length extensional bar fabricated from a multi-domain, [001] oriented and poled PMN- 0.30PT crystal revealed a monotonically decreasing Youngs modulus as a function of temperature with a sudden stiffening near 85°C corresponding to a ferroelectric rhombohedral (F R )-ferroelectric tetragonal (F T ) transition. Quasi-static, zero field stress-strain response revealed an elastic instability of the F R near 30 MPa compression. This instability is attributed to a ferroelectric rhombohedral (F R )–ferroelectric orthorhombic (F O ) transition. A dc bias field of 0.59 MV/m stabilized the F R state up to 40 MPa compressive stresses. The implications of these results on sonar projector design and performance will be discussed.

Analysis on Loss Anisotropy of Piezoelectrics with ∞ mm Crystal Symmetry

The key factor for the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components for piezoelectric vibrators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the figure of merit in the sense of loss or heat generation. In this paper, quality factors of resonance and antiresonance for both k31 and k33 vibration modes are derived, and the method to determine loss factors in various directions is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of polycrystalline ceramics, and ten different loss factors can be obtained from the measurements. Finite element simulations are made to prove the theory, and the analysis also demonstrates the significance of the piezoelectric loss factor which has usually been neglected by previous piezoelectric device designers.