Electric field effects in RUS measurements

Much of the power of the Resonant Ultrasound Spectroscopy (RUS) technique is the ability to make mechanical resonance measurements while the environment of the sample is changed. Temperature and magnetic field are important examples. Due to the common use of piezoelectric transducers near the sample, applied electric fields introduce complications, but many materials have technologically interesting responses to applied static and RF electric fields. Non-contact optical, buffered, or shielded transducers permit the application of charge and externally applied electric fields while making RUS measurements. For conducting samples, in vacuum, charging produces a small negative pressure in the volume of the material - a state rarely explored. At very high charges we influence the electron density near the surface so the propagation of surface waves and their resonances may give us a handle on the relationship of electron density to bond strength and elasticity. Our preliminary results indicate a charge sign dependent effect, but we are studying a number of possible other effects induced by charging. In dielectric materials, external electric fields influence the strain response, particularly in ferroelectrics. Experiments to study this connection at phase transformations are planned. The fact that many geological samples contain single crystal quartz suggests a possible use of the piezoelectric response to drive vibrations using applied RF fields. In polycrystals, averaging of strains in randomly oriented crystals implies using the “statistical residual” strain as the drive. The ability to excite vibrations in quartzite polycrystals and arenites is explored. We present results of experimental and theoretical approaches to electric field effects using RUS methods.     

Excess low frequency conduction noise in a granular composite

Granular composites consisting of 25% nickel as 8 nm diameter particles dispersed in an aluminium oxide matrix display excess conduction noise. Co-deposited films with resistance per square about 10⁵ ohms and negative temperature coefficient show a noise power spectral density $\text{S}{}_{\mathrm{v}}\text{(?) =}\text{S}{}_{\mathrm{v}}\text{(1)}\text{?}{}^{\mathrm{\alpha }}$ where α ? 1.10 ± 0.03 over the accessible spectral range of 0.1 Hz ? ? ? 5000 Hz. The amplitude 3 × 10^?15 ? S_v(1) ? 5 × 10^?12 V²Hz^?1, appears to increase approximately quadratically as the applied voltage V_s up to V_s ? 2.5 V and as the first power of V_s for 2.5 ? V_s < 35 V.     

New reactive polymers containing nitrogen functionalities: From asymmetric synthesis to supported catalysis

Several new reactive polymers containing various nitrogen functionalities have been prepared in bead form and tested as catalysts or ligands for reactive moieties in organic synthesis. In particular polymers containing 4-dialkylaminopyridine pendant groups show good to excellent catalytic activities depending on their structure and their microenvironment. Best results are obtained on polystyrene backbones when the catalytic species are removed from the styrene rings by a three carbon spacer. Poly-benzimidazole resins prepared by precipitation polymerization are good ligands for transition metal catalysts used in the catalytic hydrogenation of nitro compounds or olefinic double-bonds. The PBI resins can also be used to prepare a polymeric oxidizing reagent through the binding of Cr(VI); the reagent oxidizes alcohols to the corresponding carbonyls while spent Cr(II) or Cr(III) remains anchored to the polymer. Other polymers containing chiral amino-alcohol pendant groups show useful properties as chiral auxiliaries in the asymmetric reduction of ketones using polymer-complexed lithium aluminium hydride.