Hu Cao

Dielectric and piezoelectric performance of PMN-PT single crystals with compositions around the MPB: influence of composition, poling field and crystal orientation

Abstract This paper presents a detailed study of the dependence of the dielectric and piezoelectric performance on the composition, poling field and crystallographic direction for Pb(Mg 1/3 Nb 2/3 )O 3 ue5f8PbTiO 3 (PMN–PT) single crystal plates with compositions around the rombohedral–tetragonal morphotropic phase boundary (MPB). The Tmax of the plates lies in the range of 130–160xa0°C. Influence of poling field in a range of 0–3 kV mm −1 on their properties was investigated. Under appropriate poling conditions and with proper compositions, the plates show excellent piezoelectric property with d 33 larger than 1800 pC N −1 along 〈001〉 and 〈011〉, and 1300 pC N −1 along 〈111〉, respectively. It is also suggested that the relaxor nature of PMN, the domain structure modulation and the MPB effect all play important roles in influencing the piezoelectric performance. The possibility of the existence of the induced orthorhombic or monoclinic phase is also discussed in this paper.

Crystal orientation dependence of dielectric and piezoelectric properties of tetragonal Pb(Mg1/3Nb2/3)O3-38%PbTiO3 single crystal

Abstract The crystallographic orientation dependence of the P–E behavior and dielectric and piezoelectric properties in tetragonal Pb(Mg 1/3 Nb 2/3 )O 3 –38%PbTiO 3 (PMNT62/38) single crystals were investigated. When the electric field was applied to 15xa0kV/cm the coercive electric fields E c varied from E c [0 0 1] ∼8.25 to E c [1 1 0] ∼6.80 to E c [1 1 1] ∼4.11 xa0kV/cm and the remnant polarizations were P r [0 0 1] ∼34.25 , P r [1 1 0] ∼22.64 , and P r [1 1 1] ∼18.87 xa0μC/cm 2 . In [1xa01xa00] and [1xa01xa01] poled crystals, the formation of the engineered domain configuration caused more enhanced dielectric and piezoelectric activities: d 33[1 1 0] ∼1350 xa0pC/N and e r [1 1 0] ∼6972 ; d 33[1 1 1] ∼980 xa0pC/N and e r [1 1 1] ∼9784 , compared with d 33[0 0 1] ∼350 xa0pC/N and e r [0 0 1] ∼760 at room temperature.

Neutron and x-ray diffraction study of cubic [111] field-cooled Pb(Mg1/3Nb2/3)O3

Neutron and x-ray diffraction techniques have been used to study the competing long- and short-range polar order in the relaxor ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3} (PMN) under a [111] applied electric field. Despite reports of a structural transition from a cubic phase to a rhombohedral phase for fields E>1.7 kV/cm, we find that the bulk unit cell remains cubic (within a sensitivity of 90 deg. -{alpha}=0.03 deg.) for fields up to 8 kV/cm. Furthermore, we observe a structural transition confined to the near surface volume or skin of the crystal where the cubic cell is transformed to a rhombohedral unit cell at T{sub c}=210 K for E>4 kV/cm, for which 90 deg. -{alpha}=0.08{+-}0.03 deg. below 50 K. While the bulk unit cell remains cubic, a suppression of the diffuse scattering and concomitant enhancement of the Bragg peak intensity is observed below T{sub c}=210 K, indicating a more ordered structure with increasing electric field yet an absence of a long-range ferroelectric ground state in the bulk. The electric field strength has little effect on the diffuse scattering above T{sub c}, however, below T{sub c} the diffuse scattering is reduced in intensity and adopts an asymmetric line shape in reciprocal space. Themorexa0» absence of hysteresis in our neutron measurements (on the bulk) and the presence of two distinct temperature scales suggests that the ground state of PMN is not a frozen glassy phase as suggested by some theories but is better understood in terms of random fields introduced through the presence of structural disorder. Based on these results, we also suggest that PMN represents an extreme example of the two-length scale problem, and that the presence of a distinct skin may be necessary for a relaxor ground state.«xa0less

Dynamic origin of the morphotropic phase boundary : Soft modes and phase instability in 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3

We report neutron inelastic scattering on single crystal 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material that lies within the compositional range of the morphotropic phase boundary (MPB). Data were obtained between 100 K and 600 K under zero and non-zero electric field applied along the cubic [001] direction. The lowest energy, zone-center, transverse optic phonon is strongly damped and softens slowly at high temperature; however the square of the soft mode energy begins to increase linearly with temperature as in a conventional ferroelectric, which we term the soft mode recovery, upon cooling into the tetragonal phase at TC. Our data show that the soft mode in PMN-0.32PT behaves almost identically to that in pure PMN, exhibiting the same temperature dependence and recovery temperature even though PMN exhibits no well-defined structural transition (no TC). The temperature dependence of the soft mode in PMN-0.32PT is also similar to that in PMN-0.60PT; however in PMN-0.60PT the recovery temperature equals TC. These results suggest that the temperature dependence and the energy scale of the soft mode dynamics in PMN-xPT are independent of concentration on the Ti-poor side of the MPB, but scale with TC for Ti-rich compositions. Thus the MPB may be defined in lattice dynamical terms as the concentration where TC first matches the recovery temperature of the soft mode. High-resolution x-ray studies show that the cubic-to-ferroelectric phase boundary shifts to higher temperatures by an abnormal amount within the MPB region in the presence of an electric field. This suggests that an unusual instability exists within the apparently cubic phase at the MPB.

Dielectric and piezoelectric properties for 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 single crystals

Abstract The dielectric and piezoelectric properties of 0.62Pb(Mg 1/3 Nb 2/3 )O 3 –0.38PbTiO 3 single crystal (PMNT62/38) were investigated in this work. Power X-ray diffraction demonstrated PMNT62/38 had a tetragonal structure at room temperature. The Curie temperature was 187xa0°C on heating. The poled and as-grown dielectric constants e r of [001] oriented PMNT62/38 at room temperature were ∼500 and ∼5000, respectively. The remanent polarization P r and coercive field E c for [001] oriented one were 34.2 μC/cm 2 and 8.25 kV/cm, respectively. The strain at 15 kV/cm and −15k V/cm were 0.078 and 0.125%, respectively. The piezoelectric constant d 33 was ∼350 pC/N. The electromechanical coupling coefficients; 0.89 of k 33 , 0.61 of k t , 0.46 of k 31 and 0.45 of k 15 were calculated from measured resonance and anti-resonance frequencies by impedance resonance techniques. In single domain process it was found the re-oriented domains of [001] poled PMNT62/38 were instable, which caused it hard to align the spontaneous polarizations to create a single domain crystal.

Intermediate ferroelectric orthorhombic and monoclinicMBphases in [110] electric-field-cooledPb(Mg1∕3Nb2∕3)O3–30%PbTiO3crystals

Office of Naval Research under Grant Nos. N000140210340, N000140210126, MURI N0000140110761