Continuous functionally graded material to improve the thermoelectric properties of ZnO

Corson L. Cramer, Jesus Gonzalez-Julian, Paul S. Colasuonno, Troy B. Holland

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

Functionally graded material (FGM) in terms of grain size gradation is fabricated from ZnO with a combination of modified Spark Plasma Sintering (SPS) graphite tooling, water sintering enhancements through transient liquid phase surface transport, and strategic SPS mechanical loading. The grain size gradation of the ZnO FGM spans from 180 nm grains to 1.2 micrometers in a fully dense material. This is the first semiconductor or ceramic to be graded microstructurally to this extent. Predictions of the microstructure with a Master Sintering Curve (MSC) approach were done with a series of isothermal experiments on two different FGM conditions revealing a slight offset due to a constrained mechanism. The mechanical properties were tested with Vickers micro hardness across the sample, showing a gradient in hardness from 2.6 GPa to 4.2 GPa. In addition, the thermoelectric properties of the FGM were measured and show a zT of 2 × 10−5 at 100 °C compared to uniform small- and large-grained samples of 1 × 10−6. This is an order of magnitude difference making a new path for improvements of bulk thermoelectric material.

Original languageEnglish
Pages (from-to)4693-4700
Number of pages8
JournalJournal of the European Ceramic Society
Volume37
Issue number15
DOIs
StatePublished - Dec 2017
Externally publishedYes

Keywords

  • Differential constrained sintering
  • Functionally graded material
  • Thermoelectrics

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