Large Piezoelectric Response and Ferroelectricity in Li and V/Nb/Ta co-doped w-AlN

<div>Based on density functional theory, we show that Li and</div><div>X (X=V, Nb and Ta) co-doping in 1Li:1X ratio broadens the</div><div>compositional freedom for significant piezoelectric enhancement in w-AlN, promising them to be good alternatives of expensive Sc. Interestingly, these co-doped w-AlN also show quite large spontaneous electric polarization about 0.80 C/m2 with the possibility of ferroelectric polarization switching, opening new possibilities in wurtzite nitrides. Increase in piezoelectric stress constant (e33) with decrease in elastic constant ( C33 ) results enhancement in piezoelectric strain constant ( d33 ), which is desired for improving the performance of resonators for high frequency RF signals. Also, these co-doped w-AlN are potential lead-free piezoelectric materials for energy harvesting and sensors as they improve the longitudinal electromechanical coupling constant (K^2 33), transverse piezoelectric strain constant (d31), and figure of merit for power generation. However, the enhancement in K^2 33 is not as pronounced as that in d33, because co-doping increases the dielectric constant. The longitudinal acoustic wave velocity (7.09 km/s) of Li0.1875Ta0.1875Al0.625N is quite comparable with that of commercially used piezoelectric LiNbO3 or LiTaO3 in special cuts (about 5~7 km/s) despite the fact that the acoustic wave velocities drop with co-doping or Sc concentration.</div>

Large Piezoelectric Response and Ferroelectricity in Li and V/Nb/Ta co-doped w-AlN

<div>Based on density functional theory, we show that Li and</div><div>X (X=V, Nb and Ta) co-doping in 1Li:1X ratio broadens the</div><div>compositional freedom for significant piezoelectric enhancement in w-AlN, promising them to be good alternatives of expensive Sc. Interestingly, these co-doped w-AlN also show quite large spontaneous electric polarization about 0.80 C/m2 with the possibility of ferroelectric polarization switching, opening new possibilities in wurtzite nitrides. Increase in piezoelectric stress constant (e33) with decrease in elastic constant ( C33 ) results enhancement in piezoelectric strain constant ( d33 ), which is desired for improving the performance of resonators for high frequency RF signals. Also, these co-doped w-AlN are potential lead-free piezoelectric materials for energy harvesting and sensors as they improve the longitudinal electromechanical coupling constant (K^2 33), transverse piezoelectric strain constant (d31), and figure of merit for power generation. However, the enhancement in K^2 33 is not as pronounced as that in d33, because co-doping increases the dielectric constant. The longitudinal acoustic wave velocity (7.09 km/s) of Li0.1875Ta0.1875Al0.625N is quite comparable with that of commercially used piezoelectric LiNbO3 or LiTaO3 in special cuts (about 5~7 km/s) despite the fact that the acoustic wave velocities drop with co-doping or Sc concentration.</div>

Uncovering ferroelectric polarization in tetragonal (Bi1/2K1/2)TiO3–(Bi1/2Na1/2)TiO3 single crystals

We report the robust ferroelectric properties of (1 − x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (x = 33%) single crystals grown by a top-seeded solution growth process under a high oxygen-pressure (0.9 MPa) atmosphere. The sample exhibit a large remanent polarization of 48 μC/cm2 and a sizeable piezoelectric strain constant of 460 pm/V. Neutron powder diffraction structural analysis combined with first-principles calculations reveals that the large ferroelectric polarization comparable to PbTiO3 stems from the hybridization between Bi-6p and O-2p orbitals at a moderately negative chemical pressure.

Effects of Coupling Agents on the Structure and Electrical Properties of PZT-Poly(vinylidene fluoride) Composites

PZT-Poly(vinylidene fluoride) composites were prepared by hot-pressing method. Before addition, PZT particles were firstly modified with two different coupling agents. The micromorphology, microstructure, dielectric properties, and piezoelectric properties of the composites were characterized and investigated. Results indicated that PZT&nbsp;particles were homogeneously dispersed in the PVDF matrix by the addition of coupling agents. The electric properties of PZT-PVDF&nbsp;composites with NDZ-101 were the best. Especially when the volume ratio of the titanate coupling agent NDZ-101 was 1%, the piezoelectric strain constant d33 of PZT-PVDF composites reached maximum value 19.23pC/N; its relative dielectric constant &epsilon;r was 67.45; at the same time its dielectric loss tan&delta; was 0.0766.

Fabrication of Piezoelectric-Rubber of Large Piezoelectric Property

ABSTRACTIn the previous investigation, piezoelectric properties of the ‘Aligned-type’ in which the piezoelectric-ceramic particles are formed in linear aggregates in the rubber, remarkable piezoelectric properties were confirmed. In this investigation, to further enhance the piezoelectric properties of the Aligned-type, the influence of the matrix properties was investigated. The properties on which we focused were the dielectric constant and the Young’s modulus. Four kinds of matrix materials whose dielectric constant and Young’s modulus are different from each other; Silicone gel, Silicone rubber, Urethane rubber and Poly-methyl-methacrylate were investigated. As a result of measurement of the piezoelectric strain constant d33 of the Aligned-Type, it was confirmed that though the influence of the dielectric constant of the matrix material was small, the lower the Young’s modulus of the matrix was, the higher d33 was.

Piezoelectric Properties and Electric Field-Induced-Strains of Textured (Bi1/2K1/2)TiO3- BaTiO3 Ceramics

Grain-oriented 0.8(Bi1/2K1/2)TiO3-0.2BaTiO3 (BKT-BT20) ceramics were prepared by the Reactive Templated Grain Growth (RTGG) method. The BKT-BT20 ceramics sintered at 1070°C for 100 h. The grain-oriented BKT-BT20 exhibited relatively high orientation factor, F, of 0.87 and density ratio of 92%. A resistivity of textured BKT-BT20 was 1.29×1013 Ωcm. Piezoelectric strain constant, d33, and the normalized strain, d33*, of the textured BKTBT20 ceramic in the direction parallel (//) to the tape stacking direction were 117 pC/N and 243 pm/V (at 80 kV/cm), respectively.

ENHANCED PIEZOELECTRIC PROPERTIES IN (Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 FERROELECTRIC SINGLE CRYSTALS

Single crystals of x( Bi,K ) TiO 3 - (1 - x)( Bi,Na ) TiO 3 (0.11 ≤ x ≤ 0.47) were grown by a flux method and their polarization and piezoelectric properties were investigated along 〈100〉 cubic at 25°C. Rietveld analysis of powder X-ray diffraction data provides a tentative phase diagram in this system: rhombohedral R3c for x ≤ 0.22, pseudocubic for 0.22 < x < 0.3 and tetragonal P4mm for 0.3 ≤ x. Piezoelectric strain properties show that the crystals (x = 0.38) exhibited an extremely large piezoelectric strain constant of 637 pm/V.

Influence of La2O3 Doping Amount on Properties of NBT-KBT-BT Lead-Free Piezoelectric Ceramics

0.85(Na0.5Bi0.5)TiO3-0.144(K0.5Bi0.5)TiO3-0.006BaTiO3(NBT-KBT-BT) lead-free piezo -electric ceramics were prepared using conventional solid state method. The influence of La2O3 doping amount on the crystal phase, surface microstructure and properties of the NBT-KBT-BT lead free piezoelectric ceramics were investigated using X-ray diffraction(XRD), Scanning electron microscopy(SEM) and other analytical methods. The results show that La2O3 has diffused into the lattice of NBT-KBT-BT ceramics. Consequently, a pure perovskite phase is formed. SEM images show that the microstructure of the ceramics is changed with the addition of a small amount of La2O3, La2O3 doping can make grain growing. The piezoelectric strain constant(d33) starts increasing and then decreasing, the dielectric constant(εT33/ε0) increases continuously and the dielectric loss(tanδ) starts increasing and then decreasing and then increasing when La2O3 doping amount increases. When the doping amount of La2O3 is 0.4wt.% and the sintering temperature is 1160°C, the NBT-KBT-BT piezoelectric ceramics with good comprehensive properties can be obtained. Its piezoelectric strain constant(d33), dielectric constant(εT33/ε0), and dielectric loss(tanδ) are 151pC/N, 1543 and 4.2%, respectively.

Effects of Barium Substitution on the Structure and Properties of PSZT Piezoelectric Ceramics

Piezoelectric ceramics with appropriate curie temperatures and high dielectric and piezoelectric performances are attractive for formations of ceramic/polymer piezoelectric composites. The PSZT ceramics with compositions of 0.98Pb1.0-xBaxTi0.48Zr0.52O3-0.02PbSbO3 (x=0.14~0.24) have been prepared by a conventional solid reaction process. The ceramic structures are analyzed by X-ray diffraction and the barium substitution leads to structural changes of the tetragonal and rhombohedral phases which constitute the perovskite PSZT ceramics, and lattice distortions. The curie temperature almost linearly decreases from 226 °C to 141 °C corresponding the barium content increases from 0.14 to 0.24 in the ceramics. The dielectric and piezoelectric properties are largely influenced by the barium substitution and when the barium content at vicinity of 0.22, the piezoelectric strain constant d33 exhibits a dramatic change. It is found that as the barium content around 0.22, the PSZT ceramic specimen is characterized with a low curie temperature Tc=156 °C, and satisfied dielectric and piezoelectric properties with the relative dielectric constant εr=5873, dielectric loss factor tanδ=0.0387, piezoelectric strain constant d33=578 pC/N.

Influence of Strontium Ferrite on Properties of 0-3 Cement-Based Piezoelectric Composites

0-3 cement based piezoelectric composites were fabricated using sulphoaluminate cement as matrix by compressing technique method. The effects of strontium ferrite content on the piezoelectric properties, dielectric properties and acoustic impedance of the composites were studied. The results show that the piezoelectric strain constant d33 and piezoelectric voltage constant g33 of the composites increase gradually with increaing strontium ferrite content. When the strontium ferrite mass fraction is 0.4%, both of the piezoelectric strain constant d33 and piezoelectric voltage constant g33 of the composite have the maximum value, and the values are 16.6pC•N-1 and 31.4mV•m•N-1, which are 35% and 19% larger than that of the composite without strontium ferrite doped, respectively. With the strontium ferrite content increase, both of the dielectric constant εr and the dielectric loss tanδ of the composites increase. With the addition of strontium ferrite the acoustic impedance Z increases, but there is no obvious relation between the strontium ferrite content and Z.