Defects and Grain boundaries have a remarkable effect on the thermal and electrical transport properties of polycrystalline materials but are often ignored by prevailing physical theories. Point defects can be altered with phase boundary mapping and processing engineered with defect thermodynamics. Grain boundaries and interfaces can adversely alter the properties of Power Electronics, Solar Cells, Batteries and Thermoelectrics such as interfacial electrical and thermal resistance (Kapitza resistance) and even an interfacial Seebeck effect. Interfacial thermal resistance limits the performance of power electronics because of overheating. New scanning thermal reflectance techniques can image the thermal resistance of interfaces and boundaries directly. The Thermal conductivity suppression at grain boundaries can even be imaged showing that different grain boundaries can have very different thermal resistances with high energy grain boundaries having more resistance and low energy boundaries having lower thermal resistance. Electrical grain boundary resistance can be so high in some thermoelectric materials it is the dominant property that limits zT. While small grains are usually considered beneficial for thermoelectric performance due to reduced thermal conductivity, Mg₃Sb₂ based thermoelectric materials, so far at least, contradict that trend. Indeed, atomic segregation has been recently observed at the nanometer scale in grain boundaries in many materials suggesting interfacial or complexion phases should be specifically considered when understanding nearly all thermoelectric materials. The concentration of point defects, such as vacancies, interstitial and substitutional atoms can now be predicted with DFT allowing defects to be included in phase diagram analysis for prediction of materials processing for particular properties.

G. Jeffrey Snyder教授是一位在热电材料研究领域具有重要影响力的科学家，担任美国西北大学材料科学与工程学院的终身教授。他在电子能带结构工程和热电性能微观结构工程方面提出了创新方法，并因此在学术界获得了极高的声誉。Snyder教授的研究成果丰富，在包括Science（4）、Nature（1）、Nature Materials（8）、Joule（6）在内的国际顶尖科学期刊上发表论文近900篇，被引用次数接近90,000次。他的h-index为135，反映了他的研究工作的广泛影响力和深远意义。