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Updated: Sep 18, 2025
Synthesis and Microdiffraction at Extreme Pressures and Temperatures
Published on: October 7, 2013
Synthesis, Stability, and Crystal Structure of CaTi2O4-Type ZnCr2O4: High-Pressure Crystal Chemistry of Postspinel
Takayuki Ishii1, Yudai Masaki2, Alan B Woodland3
1Institute for Planetary Materials, Okayama University, Misasa, 682-0193 Tottori, Japan.
Abstract:
High-pressure phases of spinel-type A2+B23+O4, called postspinel phases, have been of great interest in materials science for the appearance of novel physical properties and geoscience for understanding the Earth's deep interior. The CaFe2O4- and CaTi2O4-structured phases are representative postspinel phases. To design a postspinel phase, it is useful to construct a prediction diagram using crystallographic parameters such as ionic radius. Especially, the appearance of the CaTi2O4-type phase is rare in high-pressure-temperature space, and therefore, its further exploration is desired to develop its material group. Our previous study constructed a structural prediction diagram of A2+B23+O4 postspinel phases based on ionic radii. Based on the prediction diagram, we here investigated the system ZnCr2O4 at high-pressure-temperature conditions to explore the stability field of the CaTi2O4-type phase. We found that the spinel-type phase transformed to the CaTi2O4-structured phase at 23-24 GPa and 1000-1400 °C. Rietveld structure analysis of the recovered high-pressure phase yielded lattice parameters for the CaTi2O4-type phase of a = 2.8634(1) Å, b = 9.4990(4) Å, c = 9.7568(3) Å, and Z = 4 (space group: Cmcm). Thus, our prediction diagram with ionic radii successfully predicted the structure types of an A2+B23+O4 postspinel phase and is therefore useful to design a novel postspinel phase.
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