Walter R. Olson

Chemically prepared lead magnesium niobate dielectrics

A chemical solution powder synthesis technique has been developed that produces fine uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions.

Raman study of lead zirconate titanate under uniaxial stress

The authors used micro-Raman spectroscopy to monitor the ferroelectric (FE) to antiferroelectric (AFE) phase transition in PZT ceramic bars during the application of uniaxial stress. They designed and constructed a simple loading device, which can apply sufficient uniaxial force to transform reasonably large ceramic bars while being small enough to fit on the mechanical stage of the microscope used for Raman analysis. Raman spectra of individual grains in ceramic PZT bars were obtained as the stress on the bar was increased in increments. At the same time gauges attached to the PZT bar recorded axial and lateral strains induced by the applied stress. The Raman spectra were used to calculate an FE coordinate, which is related to the fraction of FE phase present. The authors present data showing changes in the FE coordinates of individual PZT grains and correlate these changes to stress-strain data, which plot the macroscopic evolution of the FE-to-AFE transformation. Their data indicates that the FE-to-AFE transformation does not occur simultaneously for all PZT grains but that grains react individually to local conditions.

Interrogating adhesion using fiber Bragg grating sensing technology

The assurance of the integrity of adhesive bonding at substrate interfaces is paramount to the longevity and sustainability of encapsulated components. Unfortunately, it is often difficult to non-destructively evaluate these materials to determine the adequacy of bonding after manufacturing and then later in service. A particularly difficult problem in this regard is the reliable detection/monitoring of regions of weak bonding that may result from poor adhesion or poor cohesive strength, or degradation in service. One promising and perhaps less explored avenue we have recently begun to investigate for this purpose centers on the use of (chirped) fiber Bragg grating sensing technology. In this scenario, a grating is patterned into a fiber optic such that a (broadband) spectral reflectance is observed. The sensor is highly sensitive to local and uniform changes across the length of the grating. Initial efforts to evaluate this approach for measuring adhesive bonding defects at substrate interfaces are discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Miniaturized domain engineered multilayer actuators

PMN/PT 67/33 <100> single crystals were evaluated under high drive conditions from ambient to 80/spl deg/C for miniaturized multilayer actuator (MLA) applications. Multilayer actuators were fabricated under identical processing conditions using two different materials: (1) single crystal PMN/PT (SCPMN) and (2) hot-pressed PZT-5A. Five layer SCPMN actuators with individual element sizes of 3 mm/spl times/3 mm/spl times/0.25 mm have measured displacements on the order of 3 /spl mu/m at 20 kV/cm unipolar field. While superior strain behavior was observed for the PMN/PT single crystals at ambient, at higher operating temperatures (50/spl deg/C to 80/spl deg/C), the performance declined. Insights into both device performance and the different physics governing normal ferroelectric and domain engineered materials with temperature were obtained by two techniques: (1) high field ac impedance analysis (0.6 to 8 kV/cm ac) and (2) analysis of dielectric transformation behavior with hydrostatic pressure (0 to 2 GPa).

Experiments investigating the effects of the accelerating gap voltage pulse on the ion focused (IFR) high current electron recirculators

The authors have established experimentally that pulsing the accelerating gap of the ET-2 cavity puts the electrons and ions of the ion focusing regime (IFR) plasma channel into motion. As a result of the electron motion, two types of disturbances propagate axially into opposite directions: (1) electrons move to the left of the gap, and (2) a sheath moves to the right (direction of gap electric field). Both disturbances cause the Rogowski coils to register a 200-300-A current in the same direction. The argon ions of the IFR channel escape radially with velocities equal to 1.2*10/sup 7/ cm/s and take 400 ns to hit the 5-cm-radius pipe. Cusp magnetic fields or possibly transparent grids upstream and downstream from the accelerating gap can decouple it from the IFR channel.<<ETX>>