MSE Department Seminar

Pyroelectric infra-red (PIR) sensors have a number of advantages over other IR sensors, including room-temperature operation, wide wavelength sensitivity and low cost, leading to their use in many applications, including intruder alarms, footfall counting, automatic light switches, gas analysis, fire/flame detection and thermal imaging. PIR’s had a market of ca US$50 million in 2020, expected to reach US$68 million by 2025, or about 10% of the total infrared detector market.

Phase separation in the H2O-SiO2 system is examined in view of immiscibility in the alkali and alkaline earth silicates, critical parameters of which correlate with the charge and size of network modifier cations. Although the miscibility gaps of the H2O-SiO2 system have not been completely characterized, available data indicate a phase separation tendency greater than that of Li2O-SiO2, consistent with H+ being smaller than Li+.

High-fidelity physics-based simulations have been widely developed to study complex physical systems. Despite its interpretability and accuracy, physics-based simulations usually have two limitations: a) running high-fidelity simulations often requires high computational cost and consumes a large amount of time; b) most of the simulations are built upon deterministic methods that is insufficient for uncertainty quantification (UQ) when modeling complex systems with various types of uncertainties.

The static structure-property relationship is central to materials science. What happens to the properties when the structure keeps evolving? In many cases, the mechanical and electronic properties are determined by the instantaneous lattice structure, but this may not always be true. In particular, a qualitative distinction can be made by atomic motions called “chiral phonons”, which breaks time-reversal symmetry on average, and would in principle affect all properties protected by such symmetry.

This talk will review two recent projects that cover: 1) microstructural modeling of Ni-based super alloys during additive manufacturing and 2) image-driven-machine-learning techniques for characterizing nuclear materials during a complex series of processing steps. The microstructure modeling work focuses on linking length scales from individual dendrites to macroscopic heat flows during laser processing.

Calorimetry has long been used to study chemical reactions and phase transitions in materials. The technique finds its origin in the mid-18th century when Scottish physician Joseph Black discovered the notion of latent heat and Lavoisier developed an ice calorimeter to measure the amount of heat given off during combustion of carbon or respiration of living organisms.

Polar crystals display pyroelectricity upon temperature change with two primary and secondary contributions. Primary pyroelectricity, arises directly from the anharmonicity of chemical bonds, leading, upon heating or cooling, to changes of the relative positions of the atoms without changing the overall volume of the crystal. The secondary pyroelectricity arises from the thermal expansion or contraction of the crystal, i.e. a piezoelectric contribution.

Complex-oxide materials possess a range of interesting properties and phenomena that make them candidates for next-generation devices and applications. But before these materials can be integrated into state-of-the-art devices, it is important to understand how to control and engineer their response in a deterministic manner.

Semiconductors are the most important part of the electronics for the modern society. A good semiconductor should have a right band gap, high carrier mobility in both electrons and holes, etc., but semiconductors with larger band gap, higher carrier mobility, higher thermal conductivity, better matched coefficient of thermal expansion, etc. are very much needed for the future. Boron arsenide (BAs) seems to be the ideal semiconductor we are dreaming of.

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations and heat. This presentation provides an overview of piezoelectric harvesting system along with the closely related sub-classes of pyroelectrics and ferroelectrics.