Dear Sir. Concerning your issue about how to make a ZnO prism. Formation of ZnO single crystal hexagonal prisms from a sol-gel method is presented. The method required water, zinc acetate, and ethanolamine to create a gel of zinc hydroxide and zinc hydroxide acetate, which upon heating formed single crystal hexagonal prisms. Characterization of the gel was done by XRD as well as XRD high temperature chamber (HTK) to determine the role of temperature in prism formation. SEM images showed hexagonal prisms were of uniform size (0.5 × 2 µm.) TEM and electron diffraction images showed a change from randomly oriented particles to an ordered single crystal after heating. Water and the acetate salt of zinc proved to be critical to prism formation. For more details, I think the following below link may help you in your issue:

http://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=4866&context=etd

http://www.freepatentsonline.com/9404195.pdf

Thanks

Dear Isam Eldin Hussein Elgailani,

thank you for your response. While you are referring to very small particles, I would like to get a prism at a macroscopic scale, on the order of 10 cm x 10 cm.

Thank you,

Sascha Grusche

I don't have direct experience, but there are links on this Wikipedia page which may be of interest - unless you have already checked them out.

https://en.wikipedia.org/wiki/Zinc_oxide#Laboratory_synthesis

Schultz et. al. describe growth of large single crystals of  ZnO using the Bridgman method: http://www.sciencedirect.com/science/article/pii/S0022024807009487

As you have probable found, much of the published material for ZnO is for thin films, powder and nanostructures.  The oxide decomposes at temperatures near the melting point, causing problems with some fabrication techniques.

Good luck.