Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.     

Synthetic Layered Silicate as a Carrier for Liquid Ingredients for the Rubber- and Tire Industry

We propose the use of novel materials based on synthetic calcium silicate hydrate (C S H) for the rubber- and tire industry. We found that the synthetic silicate belongs to the family of layered calcium silicate hydrates. Due to its layered structure and inert surface it easily adsorbs liquid components of rubber compounds, such as bis(triethoxysilylpropyl) tetrasulfide (TESPT) and liquid polysulfide (LP). Then, in processing, the C S H can smoothly release these components. The water, trapped in the material's gallery layers, plays the role of a catalyst in the silane coupling on silica's surface. In addition, we used this silicate as a component in promoter systems in order to improve adhesion stability between a brass-coated steel cord and rubber. The application of the calcium silicate hydrate as an inert substrate for the promoter system allowed the development of materials that have comparable adhesion strength with most commercial promoters.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

Role of B-site ion on proton conduction in acceptor-doped Sm2B2O(7-δ) (B = Ti, Sn, Zr and Ce) pyrochlores and C-type compounds

Proton conduction in three pyrochlores, Sm(1.92)Ca(0.08)B(2)O(7-δ), B = Ti, Sn, Zr and one phase with a related C-type fluorite superstructure, B = Ce, has been investigated. The samples were prepared by solid state reaction. Infrared spectroscopy measurements and thermogravimetric analysis were carried out to study the extent of proton dissolution and determine its dependence on the B-site ion. Electrochemical impedance spectroscopy, performed on heating and cooling pre-hydrated samples, confirmed significant levels of proton conduction for Sm(1.92)Ca(0.08)Ti(2)O(7-δ) and Sm(1.92)Ca(0.08)Sn(2)O(7-δ) up to T～ 500 °C. In comparison the B = Zr and Ce samples revealed lower levels of proton conductivity, confined to temperatures below ～ 400 °C. Proton diffusion coefficients of 3.36 × 10(-8), 1.73 × 10(-9), 5.53 × 10(-10) and 2.78 × 10(-11) cm(2) s(-1) were determined at 300 °C for samples with B = Ti, Sn, Zr and Ce respectively. The proton mobility of Sm(1.92)Ca(0.08)Ti(2)O(7-δ) is therefore approximately one order of magnitude lower than that found in yttrium-doped perovskite phases such as BaZrO(3) and BaCeO(3).     

Crystal structure of Bi(0.9)Sm(0.1)Fe(1-x)Mn(x)O3 multiferroics

Bi(0.9)Sm(0.1)Fe(1-x)Mn(x)O(3), with x=0.00, 0.15, 0.30 have been synthesised by solid-state reaction. The structures of the materials, characterised via Rietveld analysis of high resolution powder neutron diffraction data, reveal a structural transition from R3c to orthorhombic Imma symmetry is complete for the x=0.30 sample. The antiferromagnetic ordering temperature, magnitude of the ordered magnetic moment at the B-site, and the dielectric constant all decrease as a function of increasing Mn content.     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7�C�� pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7?C?? are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide $ {p_{{{{\rm{O}}_{{2}}}}}} $ range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500?C300?°C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045?S/m under wet oxygen at 500?°C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500?°C and protons becoming increasingly important below this temperature.     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7–δ pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7–δ are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide \( {p_{{{{\rm{O}}_{{2}}}}}} \) range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500–300 °C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045 S/m under wet oxygen at 500 °C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500 °C and protons becoming increasingly important below this temperature.

     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

New22Ne(α,n)25Mg-resonances at very low energies relevant for the astrophysical s-process

The ²²Ne(α,n)²⁵Mgreaction is thought to be one of the main neutron sources for the astrophysical s-process. Thus cross section data for this reaction have been obtained from near the threshold (E _α≈570keV) up toE _α=2100 keV using the 4 MV DYNAMITRON accelerator at Stuttgart, the windowless gastarget system RHINOCEROS and a 4π neutron detector. Two new resonances have been observed atE _α=623 ± 6 and 838 ± 6 kev, which dominate the reaction rate at T₉<0.3.Possible background reactions are discussed.