Pyroelectric, ferroelectric, and piezoelectric materials have been fabricated in bulk single crystals and in ceramic, thin- and thick-film, and composite forms. All of the major techniques are described depend on the applicability and convenience of fabricating bulk and MEMS-based energy harvesters. Notable examples include the following:
• Triglycine sulfate (TGS)-type crystals have great potential in pyroelectric energy-harvesting applications based on its properties. However, it has attracted limited interest, possibly due to its low Curie temperature (49 °C). It is also water soluble, hygroscopic, and relatively low strength. It is possible to use it with proper encapsulation.
• Lead magnesium niobate–lead titanate (PMN-PT) single crystals are of interest due to their ultra-high piezoelectric and pyroelectric coefficients. These materials have a low Curie temperature (121 °C), which can limit the material to relatively-low-temperature operations.
• The lead zirconate titanate (PZT) family remains a widely used commercial ceramic due to its relative ease of fabrication in polycrystalline form with good piezoelectric properties.
Other materials being explored for energy-harvesting applications include lithium tantalate (LTO) single crystals, a family of potassium sodium niobate (KNN), magnesium-doped bismuth sodium titanate-barium titanate (BNT-BT) single crystals, barium strontium titanate (BST) films, AlN, GaN, CdS, and ZnO.
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