James K. Knowles Lecture & Caltech Solid Mechanics Symposium

There are enormous reservoirs of energy stored on Earth at small temperature differences, including natural sources such as the temperature difference between ocean (~0°C) and ambient (-40° to -20°C for most of the year) in the arctic, and man-made sources like the waste heat from power plants and computers. The conversion of these to useable forms of energy challenges basic thermodynamic reasoning. Any such conversion device is of low efficiency, but is efficiency relevant when one is not paying for the heat? Some heat engines are highly efficient, but their ability to absorb significant amounts of heat in a reasonable period of time is limited. We present a new concept for the direct conversion of heat to electricity using phase transformations in multiferroic materials. Even though the concept involves neither significant applied stress nor significant shape change, mechanics plays the key role, as the reversibility of these phase transformations apparently rests on an issue of elastic compatibility.