A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

Background Neonates with pulmonary hypertension have been treated with inhaled nitric oxide because of studies suggesting that it is a selective pulmonary vasodilator. We conducted a randomized, multicenter, controlled trial to determine whether inhaled nitric oxide would reduce mortality or the initiation of extracorporeal membrane oxygenation in infants with hypoxic respiratory failure, Methods Infants born after a gestation of greater than or equal to 34 weeks who were 14 days old or less, had no structural heart disease, and required assisted ventilation and whose oxygenation index was 25 or higher on two measurements were eligible for the study. The infants were randomly assigned to receive nitric oxide at a concentration of 20 ppm or 100 percent oxygen (as a control). Infants whose partial pressure of arterial oxygen (PaO2) increased by 20 mm Hg or less after 30 minutes were studied for a response to 80-ppm nitric oxide or control gas, Results The 121 infants in the control group and the 114 in the nitric oxide group had similar base-line clinical characteristics. Sixty-four percent of the control group and 46 percent of the nitric oxide group died within 120 days or were treated with extracorporeal membrane oxygenation (P=0.006). Seventeen percent of the control group and 14 percent of the nitric oxide group died (P not significant), but significantly fewer in the nitric oxide group received extracorporeal membrane oxygenation (39 percent vs. 54 percent, P=0.014). The nitric oxide group had significantly greater improvement in PaO2 (mean [+/-SD] increase, 58.2+/-85.2 mm Hg, vs. 9.7+/-51.7 mm Hg in the controls; P Conclusions Nitric oxide therapy reduced the use of extracorporeal membrane oxygenation, but had no apparent effect on mortality, in critically ill infants with hypoxic respiratory failure. (C) 1997, Massachusetts Medical Society.

Inhaled nitric oxide in full-term and nearly full-term infants with hypoxic respiratory failure

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Hypoxic pulmonary vasoconstriction.

The physics of the photorefractive effect is briefly discussed. A coupled-mode theory is then developed to analyze the coupling of two coherent electromagnetic waves inside a photorefractive medium. Both codirectional and contradirectional coupling are considered. The coupled-mode theory is then extended to consider the case of nondegenerate two-wave mixing. A discussion of the fundamental limit of the speed of photorefractive effect is then introduced. The coupling of two polarized beams inside photorefractive cubic crystals is considered. The formulation is focused on the cross-polarization two-beam coupling in semiconductors such as GaAs. The coupling of two electromagnetic waves inside a Kerr medium and the electrostrictive Kerr effect are discussed. A new concept of nonlinear Bragg scattering is introduced. The similarity among various kinds of two-wave mixing, including stimulated Brillouin scattering and stimulated Raman scattering are pointed out. Several applications of two-wave mixing are discussed. These include photorefractive resonators, optical nonreciprocity, resonator model of self-pumped phase conjugators, real-time holography, and nonlinear optical information processing. >

Two-wave mixing in nonlinear media

Background Pulmonary hypertension is a hallmark of high-altitude pulmonary edema and may contribute to its pathogenesis. When administered by inhalation, nitric oxide, an endothelium-derived relaxing factor, attenuates the pulmonary vasoconstriction produced by short-term hypoxia. Methods We studied the effects of inhaled nitric oxide on pulmonary-artery pressure and arterial oxygenation in 18 mountaineers prone to high-altitude pulmonary edema and 18 mountaineers resistant to this condition in a high-altitude laboratory (altitude, 4559 m). We also obtained lung-perfusion scans before and during nitric oxide inhalation to gain further insight into the mechanism of action of nitric oxide. Results In the high-altitude laboratory, subjects prone to high-altitude pulmonary edema had more pronounced pulmonary hypertension and hypoxemia than subjects resistant to high-altitude pulmonary edema. Arterial oxygen saturation was inversely related to the severity of pulmonary hypertension (r = -0.50, P = 0.002). In s...

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Inhaled nitric oxide for high-altitude pulmonary edema

The elastic, piezoelectric, dielectric, elasto‐optic, and electro‐optic tensors have been determined by numerically evaluating the measurements published until now and using the additional measurements presented in this work. The dependence of the speed of two elastic waves on the applied electric field is measured yielding one electroelastic constant g13133=(95±10)NV−1 m−1. The complete set of parameters consisting of the low‐frequency clamped dielectric constants eSij, refractive indices, elastic stiffness constants at constant electric field CEijkl, piezoelectric coefficients eijk, elasto‐optic tensor at constant electric field pEijkl, and clamped electro‐optic coefficients rSijk is used to calculate effective electro‐optic coefficients and effective dielectric constants that have to be used in photorefractive experiments where the elastic deformations associated with a periodic space‐charge field have to be considered.

Materials constants of KNbO3 relevant for electro‐ and acousto‐optics

Photorefractive effects of nominally pure and iron‐doped KNbO3 crystals with concentrations between 150 and 300 ppm have been investigated. In order to optimize the photorefractive recording times and the amplitude of the refractive changes, the crystals were thermally treated with simultaneous photorefractive testing. The photoconductivity data and the photorefractive experiments (grating spacing dependence of the beam coupling gain) show that the relative influence of electron and hole contribution is altered depending on the reduction treatment. The experimental results are discussed with a two‐carrier model.

Optimization of the photorefractive properties of KNbO3 crystals

Reduced KNbO3 crystals are shown to have the fastest photorefractive response times for applications in the visible wavelength region. Grating build‐up times at cw illumination in the microsecond region are reported which allow the use of such crystals for real‐time applications. The reduction treatment and a new method for the investigation of the photorefractive homogeneity during reduction are presented.

Reduced KNbO3 crystals for fast photorefractive nonlinear optics

Photoinduced anisotropic self-diffraction in photorefractive KNbO3 has been studied It has been shown that this type of diffraction is ideally suited for spatial light modulation or incoherent-to-coherent conversion A phase grating that is photoinduced by two coherent light beams causes the diffraction of one of the beams By spatially modulating the amplitude of the phase grating with an incoherent signal beam it is possible to transfer an incoherent image onto the coherent self-diffracted beam The performance parameters of this modulator are described with a simple model

Photorefractive spatial light modulation by anisotropic self-diffraction in KNbO(3) crystals.

Photoinduced anisotropic Bragg diffraction in photorefractive coefficient KNbO3 using the electro-optic r42 = 380 pm/V has been studied. It has been demonstrated that, by using a noncritical configuration, a He–Ne laser beam with fixed incidence angle can be deflected within a range of 5.67 deg by changing the wavelength λr of the Ar+ laser beams used for recording the photorefractive grating (wavelength tuning range; 457.9 nm < λr < 514.5 nm). It is shown that for the reported interaction angles between recording and diffracted beams, the Bragg condition is noncritically fulfilled for the whole deflection range without any beam tilting being required.

E. Voit

Papers

Materials constants of KNbO3 relevant for electro‐ and acousto‐optics

Optimization of the photorefractive properties of KNbO3 crystals

Reduced KNbO3 crystals for fast photorefractive nonlinear optics

Photorefractive spatial light modulation by anisotropic self-diffraction in KNbO(3) crystals.

Optically induced variable light deflection by anisotropic Bragg diffraction in photorefractive KNbO 3