| Abstract
| - In the course of our study on a Japanese traditional stoneware called “Bizen”, we have found that ϵ-Fe2O3, which has been classically known but recently limelighted for its magnetic potentiality, crystallizes epitaxially on needlelike crystals of mullite, 3(Al,Fe)2O3·2SiO2. This interesting reaction occurred when a pellet of Bizen clay powder was covered with rice straw and then heated to 1250 °C in a stream of nitrogen containing 1−2 vol % of oxygen. It is known that mullite forms from the clay on heating and that the rice straw provides potassium to induce partial melting in the pellet surface to a depth of ∼50 µm. The ϵ-Fe2O3-on-mullite particles formed in this molten region, changing their morphology with the oxygen partial pressure. Square-columnar single-crystalline particles with prismatic ends grew to ∼0.1 × 0.1 × 0.5 µm3 at N2/O2 = 99/1, while dendritic finlike crystals of ∼0.3 × 0.1 × 0.8 µm3, which was then the biggest size ever reported, grew at N2/O2 = 98/2. The relative ϵ-Fe2O3-to-mullite orientation also changed with the oxygen partial pressure. This discovery suggests morphological controllability of this metastable but magnetically interesting iron oxide as a function of the oxygen partial pressure.
- ϵ-Fe2O3 has been found to grow epitaxially on mullite. This reaction occurred in the partially molten surface region of a pellet of the “Bizen” clay that was covered with rice straw and heated at 1250 °C. The crystalline shape, size, and relative ϵ-Fe2O3-to-mullite orientation depend on the oxygen partial pressure even in a limited range of O2/N2 = 1−2 vol %. This discovery suggests morphological controllability of this metastable but magnetically interesting iron oxide as a function of the oxygen partial pressure.
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