Wenwu Cao

Elastic, piezoelectric, and dielectric properties of multidomain 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals

The elastic, piezoelectric, and dielectric constants of 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 domain engineered single crystal were determined experimentally by using ultrasonic and resonance methods. It was confirmed that the single crystal system has large electromechanical coupling coefficient k33 (∼94%) and piezoelectric constant d33 (∼2800 pC/N) if the poling is done along the [001] of pseudocubic directions. A soft shear mode with a velocity of 880 m/s was observed in the [110] direction with displacement in [110]. Using the measured data, the orientation dependence of phase velocities and electromechanical coupling coefficients were calculated. The origin of experimental errors and their influence on measured results are also examined.

Grain size and domain size relations in bulk ceramic ferroelectric materials

Abstract A study of the ferroelastic domain size variations with grain sizes in Pb(Zr,Ti)O3[PZT] ferroelectric ceramic has been conducted. Experimental results determined by a transmission electron microscopy (TEM) study on hard and soft PZT ceramics indicate that it is possible to observe a bulk metastable domain configuration in a thinned foil. The transmission electron microscopy observations demonstrate that the domain structures formed at the paraelectric-ferroelectric phase transition are strongly dependent on the elastic boundary conditions and crystallite sizes. Statistical analysis of the domain size distributions in PZT reveals that the traditional parabolic relation between grain size and domain size is only good for a limited sizerangeof 1–10 μm. For grains size > 10 μm, the exponent tends to be smaller than 1 2 , while for grain size 1 2 . We also report the analysis on poled ceramics which reveals for the first time direct evidence for transgranular domain switching mechanisms.

THE EXTRINSIC NATURE OF NONLINEAR BEHAVIOR OBSERVED IN LEAD ZIRCONATE TITANATE FERROELECTRIC CERAMIC

The nonlinear electric and electromechanical responses of lead zirconate titanate Pb(ZrxTi1−x)O3 ceramics to an external ac electric field have been measured under different driving levels. The onset of measurable nonlinearity is observed to be accompanied by the appearance of hysteresis loops. This lossy nature suggests that the nonlinearities in a ferroelectric ceramic are generated by the domain‐wall motion. In addition, aging experiments and the bias field dependence of the threshold field (onset of nonlinearity) all indicate the extrinsic nature of the nonlinear behavior of ferroelectric ceramics. A phenomenological theory of Arlt, Dederichs, and Herbiet [Ferroelectrics 74, 34 (1987)] has been extended to include the nonlinear contributions. With only 90° wall vibration being considered, the theory leads to some basic understanding of the experimental results.

Elastic, piezoelectric, and dielectric properties of 0.955Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.45PbTiO/sub 3/ single crystal with designed multidomains

The elastic, piezoelectric, and dielectric properties of a 0.955Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.045PbTiO/sub 3/ (PZN-4.5%PT) multi-domain single crystal, poled along [001] of the original cubic direction, have been determined experimentally using combined resonance and ultrasonic methods. At room temperature, the PZN-4.5%PT single crystal has rhombohedral symmetry. After being poled along [001], four degenerate states still remain. Statistically, such a domain-engineered crystal may be treated as having an average tetragonal symmetry, and its material constants were determined based on 4 mm symmetry. It was confirmed that the electromechanical coupling coefficient k/sub 33/ for the domain-engineered samples is >90%, and the piezoelectric constant d/sub 33/ is >2000 pC/N. A soft shear mode with a velocity of 700 m/s was found in the [110] direction. From the measured experimental data, the orientational dependence of phase velocities and electromechanical coupling coefficients was calculated. The results showed that the transverse and longitudinal coupling coefficients, k/sub 31/ and k/sub 33/, reach their maximum along [110] and [001], respectively.

Back gated multilayer InSe transistors with enhanced carrier mobilities via the suppression of carrier scattering from a dielectric interface.

The back gate multilayer InSe FETs exhibit ultrahigh carrier mobilities, surpassing all the reported layer semiconductor based electronics with the same device configuration, which is achieved by the suppression of the carrier scattering from interfacial coulomb impurities or surface polar phonons at the interface of an oxidized dielectric substrate. The room-temperature mobilities of multilayer InSe transistors increase from 64 cm(2)V(-1)s(-1) to 1055 cm(2)V(-1)s(-1) using a bilayer dielectric of poly-(methyl methacrylate) (PMMA)/Al2O3. The transistors also have high current on/off ratios of 1 × 10(8), low standby power dissipation, and robust current saturation in a broad voltage range.

High frequency properties of passive materials for ultrasonic transducers

The acoustic properties of passive materials for ultrasonic transducers have been measured at room temperature in the frequency range from 25 to 65 MHz using ultrasonic spectroscopy. These materials include alumina/EPO-TEK 301 composites and tungsten/EPO-TEK 301 composites. Experimental results showed that the acoustic impedance of the composites monotonically increased with the volume fraction of the particle filler, which is in agreement with the Denavey model. The attenuation, however, peaked between 7 and 9% volume fraction of particle filler. For comparison, several other passive materials were also fabricated and measured. The results suggest that materials that possess a higher attenuation also appear to have a larger velocity dispersion.

Single-domain properties of 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals under electric field bias

We report a complete set of material properties of single-domain, relaxor-based 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 [PMN–33%PT] single crystals. Because the single-domain state is unstable in natural conditions, a bias electric field of 0.2 MV/m was applied along the dipole direction of the rhombohedral phase during the measurements. It was found that the electromechanical coupling coefficient k33 and the piezoelectric constant d33 for single-domain PMN–33%PT are 69% and 190 pC/N, respectively. Both of them are much smaller than those of multidomain PMN–33%PT poled along [001] direction. However, the shear piezoelectric constant d15 of single-domain PMN–33%PT reaches 4100 pC/N, which is much higher than that of multidomain PMN–33%PT.

Elastic, piezoelectric, and dielectric properties of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 single crystal

The elastic, piezoelectric, and dielectric constants of 0.58Pb(Mg1/3Nb2/3)O3-0.42PbTiO3 (PMN-42%PT) were determined experimentally using combined resonance and ultrasonic methods. At room temperature the PMN-42%PT single crystal has tetragonal symmetry. The measured piezoelectric constant d33 is ∼260×10−12 C/N. The electromechanical coefficients k15, k31, k33, and kt are 0.80, 0.39, 0.78, and 0.62, respectively. From the measured material constants the orientational dependence of phase velocities and electromechanical coupling coefficients was calculated. The results showed the tetragonal crystal exhibits isotropy in the X-Y plane and k15, k33, and kt reach their maxima in [001].

Short-wavelength upconversion emissions in Ho 3+ /Yb 3+ codoped glass ceramic and the optical thermometry behavior

Ho(3+)/Yb(3+) codoped glass ceramic was prepared by melt-quenching and subsequent thermal treatment. Under a 980 nm diode laser excitation, upconversion emissions from Ho(3+) ions centered at 540, 650, and 750 nm were greatly enhanced compared with those in the precursor glass. Especially, the short-wavelength upconversion emissions centered at 360, 385, 418, 445, and 485 nm were successfully obtained in the glass ceramic. An explanation for this phenomenon is given based on the fluorescence decay curve measurements. In addition, an optical temperature sensor based on the blue upconversion emissions from (5)F(2,3)/(3)K(8)→(5)I(8) and (5)F(1)/(5)G(6)→(5)I(8) transitions in Ho(3+)/Yb(3+) codoped glass ceramic has been developed. It was found that by using fluorescence intensity ratio technique, appreciable sensitivity for temperature measurement can be achieved by using the Ho(3+)/Yb(3+) codoped glass ceramic. This result makes the Ho(3+)/Yb(3+) codoped glass ceramic be a promising candidate for sensitive optical temperature sensor with high resolution and good accuracy.

Orientation dependence of piezoelectric properties of single domain 0.67Pb(Mn1/3Nb2/3)O3–0.33PbTiO3 crystals

The orientation dependence of piezoelectric properties has been calculated for 0.67Pb(Mn1/3Nb2/3)O3–0.33PbTiO3 (PMN–33%PT) single-domain crystals based on the measured full matrix properties. It is found that the maximum d33*=2411 pC/N and k33*=0.94 occur, respectively, in directions 63.0° and 70.8° from the spontaneous polarization direction. In [001] of the cubic coordinate, the rotated properties are d33*=2316 pC/N and k33*=0.93, respectively, comparable to the measured multidomain properties. The results revealed the origin of the superior electromechanical properties in [001] poled PMN–33%PT multidomain crystals as from the large d15 of the single-domain property.