An uncommon oxygen absorption/desorption behavior is reported for the cation-stoichiometric cobalt oxide, YBaCo 4 O 7 , structurally composed of two kinds of layers of corner-sharing CoO 4 tetrahedra. We have found that YBaCo 4 O 7+δ absorbs and desorbs oxygen up to δ ≈ 1.5 in a narrow temperature range below 400 °C. The oxygen uptake/release process is highly reversible, being controlled by both temperature and oxygen partial pressure. Such a large low-temperature oxygen-content tunability is of great promise in regard to applications related to, for example, oxygen storage. Materials with similar characteristics are, to a large degree, lacking today.

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Half-Heusler MNiSn (M=Ti, Zr, Hf) compounds are well-known, excellent n-type thermoelectric materials. The n-type Seebeck coefficients of ZrNiSn are reduced because of the precipitation of the metallic Heusler ZrNi2Sn phase. An excellent n-type Seebeck coefficient can be converted to p-type based on the vacancy site occupation by the solute Co atoms in the half-Heusler TiNiSn phase as well as ZrNiSn. The Heusler phase precipitates, including their precursor nano-structure in the half-Heusler matrix and the vacancy site occupation of the half-Heusler phase, are regarded as lattice defects based on the crystallographically and thermodynamically close relationship between half-Heusler and Heusler phases.