Showing papers by "Harry L. Tuller published in 2002"

Micromechanical piezoelectric device

Abstract: A micromechanical device includes a single crystal micromachined micromechanical structure. At least a portion of the micromechanical structure is capable of performing a mechanical motion. A piezoelectric epitaxial layer covers at least a part of said portion of the micromechanical structure that is capable of performing a mechanical motion. The micromechanical structure and piezoelectric epitaxial layer are composed of different materials. At least one electrically conducting layer is formed to cover at least part of the piezoelectric epitaxial layer.

Solid‐State Ionics: Roots, Status, and Future Prospects

Abstract: This review represents the authors' view of the evolution of solid-state ionics over approximately the past 100 years. A brief history, introducing milestones of the development of this discipline, is followed by a short summary of the theory of ionic conduction in the bulk and the more recently developed theory of ionic conduction at interfaces. The central part of the article gives examples of ionic-conducting materials systems with structures ranging from one- to three-dimensional disorder. Important experimental techniques for analyzing ionic conduction, including alternating-current impedance spectroscopy, direct-current coulometry, and direct-current current-voltage measurements with blocking electrodes, are also summarized. The main technological applications, that is, batteries, solid-oxide fuel cells, electrochemical sensors, electrochromic windows, and oxygen-separation membranes, are reviewed. Finally, new concepts in solid-state ionics are presented, including the investigation of new materials (such as nanostructured phases), the study of boundaries (for example, using microelectrodes), the development of computational techniques, and the connections with other classes of materials (notably magnetic and semiconducting materials).

P-n junction sensor

Abstract: A sensor including a p-n junction for subjecting under a reverse electrical bias. A conductive layer is formed across the p-n junction for providing an alternative conductive path across the p-n junction. The conductivity of the conductive layer in the presence of a selected substance in an atmosphere is different than in the absence of the selected substance, wherein the conductivity of the conductive layer is indicative of the presence or absence of the selected substance.

Electrical Conductivity in Praseodymium-Cerium Oxide

Abstract: The electrical conductivity of PrxCe1-xO2-δ (PCO) for 0 ≤ × ≤ 0.20 was examined over a wide range of temperatures and oxygen partial pressures. A defect model based on multiple Pr valence states was found to be qualitatively consistent with the observed data. A unique pO2-dependent ionic conductivity is observed at high pO2 values in compositions containing low levels of Pr (0 ≤ × ≤ 0.01). In compositions containing higher amounts of Pr (0.05 ≤ × ≤ 0.20), formation of a Pr induced impurity band results in a significant electronic conductivity at high pO2 values.

Electrical Conductivity Prediction in Langasite for Optimized Microbalance Performance at Elevated Temperatures

Abstract: The performance of the langasite-based crystal microbalance is limited due to reductions in its resistivity at high temperatures and reduced oxygen partial pressures. In this work, we utilize a recently developed defect model to predict the dependence of the ionic and electronic contributions to the total conductivity of langasite on temperature, oxygen partial pressure and acceptor and donor dopants. These results are used to select the type and concentrations of dopants expected to provide extended operating conditions for langasite-based gas sensors and crystal microbalances.

Thin Film Stoichiometry Determination by High Temperature Microbalance Technique

Abstract: The in-situ determination of small mass changes of thin films became feasible with the availability of high temperature stable microbalances. With this technique, changes of the mechanical properties of thin films deposited on piezoelectric resonators are investigated at temperatures above 500 °C by monitoring the resonance behavior of the resonators. The results are valuable for fundamental understanding of the ionic and electronic transport processes in ceramic materials and for applications such as high temperature gas sensors. This work correlates the electrical and the mechanical properties of TiO 2-x at different oxygen partial pressures. TiO 2-x films are deposited onto high temperature resonators by laser ablation and characterized by the high temperature microbalance technique as well as electrical impedance spectroscopy at 600 °C. The oxygen partial pressure dependent resonance behavior cannot be attributed solely to mass changes of the TiO 2-x film. Changes of the film's mechanical stiffness have to be taken into consideration to explain the resonance behavior. The simultaneous electrical impedance measurements indicate a n-type conduction behavior of the TiO 2-x films.

Impedance and Mott-Schottky Analysis of a Pr0.15Ce0.85O2-x Solid Solution

Abstract: The semiconductor properties of a praseodymium-cerium oxide solid solution with composition Pr0.15Ce0.85O2-x (PCO) were investigated by d.c. current-voltage and bias-dependent impedance measurements in aqueous solution. The solution data were compared with impedance values of dry cells in air. A Mott-Schottky analysis of the PCO-solution interface capacitance showed p-type semi conductivity, a flat-band potential Efb = (2.0 ± 0.1) V/NHE and an ionized acceptor density NA = 3 10 cm-3. Using these data, an electron hole mobility μh ∼ 10-5 cm2 V-1 s-1 was calculated pointing to a small polaron conduction mechanism with a hopping energy (Eh = 0.4 eV).