Fabrication of c -axis oriented polycrystalline ZnO by using a rotating magnetic field and following sintering
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Tsunehisa Kimura Department of Applied Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo 192 0397, Japan
Keizo Uematsu Department of Chemistry, Nagaoka University of Technology, Nagaoka, Niigata 940 2188, Japan (Received 15 July 2005; accepted 5 December 2005)
We succeeded in fabricating c-axis (00l) oriented ZnO ceramics by using a rotating magnetic field and a subsequent sintering treatment. The degree of orientation in the green compact was about 0.5 along (00l) on the Lotgering scale. The degree of orientation increased to 0.99 after sintering at 1573 K. Particles can also be oriented in a static magnetic field, but along the direction of the a-axis or a,b-axes (h00), (hk0). These results show that selected axes can be oriented by controlling the magnetic field. Control of the crystal form in microstructures is expected to result in improvements in and better miniaturization of functional ceramics. I. INTRODUCTION
The orientation of crystals in microstructures is an effective method for drastically improving the properties of materials.1–10 Among the various methods that are available, the use of a magnetic field has a high potential for aligning crystal grains when processing materials and does not require any physical contact.11 Progress in superconducting magnet technology has contributed to making this a practical method. The fabrication of oriented materials with weak diamagnetic susceptibilities has been reported for metals, polymers, and ceramics.12–19 Particle orientation is even possible for substances such as alumina,20,21 zinc oxide,22 bismuth titanate,23,24 etc.,25,26 that have very low magnetic susceptibilities (
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