Subventions et des contributions :

Subvention ou bourse octroyée s'appliquant à plus d'un exercice financier. (2017-2018 à 2022-2023)

High Permittivity materials are of great interest because of important existing applications in cell phone networks and potential applications in electrostatic energy storage devices (capacitors). To be of potential use in capacitors, a material will require "giant permittivity" that is temperature independent. To be of potential use in a dielectric resonator, which is a common component in cell phone networks, the energy "loss" must be minimized, while maintaining a reasonably high and temperature-independent permittivity. This research proposal will address fundamental questions regarding both of these applications. Since 2013, giant permittivity has been thought to have been observed in two novel materials: "co-doped oxides" in which the permittivity increase is due to “defect dipoles” and "high entropy oxides" in which the permittivity increase is not understood. Recent tests have suggested that the observation of giant permittivity in co-doped oxides is strongly affected by electrical contacts. The open question as to whether “defect dipoles” can actually increase permittivity will be studied using a contact-free technique in compensated silicon. If this mechanism is demonstrated, it may lead to the development of co-doped higher band gap materials which may be useful in energy storage. We will also perform tests in the high entropy oxides, to see if previous observations of giant permittivity made by measuring capacitance at low frequency are similarly affected by electrical contacts. Turning to dielectric resonator materials, note that the lowest loss material commonly used, the ordered perovskite BaMg 1/3 Ta 2/3 O 3 , is extremely expensive because it incorporates tantalum. Many researchers have proposed using niobium-based materials to replace expensive tantalum. However, the loss mechanisms in the niobium-based materials are poorly understood. For example, while the loss in BaMg 1/3 Nb 2/3 O 3 has been predicted to be good enough for resonator applications, the losses observed in samples produced up to this point in time have been very large. Funds requested in this proposal will be used to perform a systematic study of dielectric loss in niobium-based dielectric resonator materials using a combination of x-ray diffraction and wide-frequency-range dielectric spectroscopy. The goal is to understand whether chemical composition and processing conditions can be slightly modified to decrease loss. Developing a niobium based material that could compete with tantalum based materials in terms of performance and price would be a significant and useful achievement.