Thermal materials with low thermal resistance, high melting point, and non conductive

Hi everyone.

I am working on a project, require to build a heat sink with non-conductive material. Are there any materials on the market, with low thermal resistance, high melting point (>1000C) like metal, but non-conductive?

Thanks.

Search here by specifying your requirements like Melting point, Electrical resistivity and Thermal conductivity.
Search Engineering Material by Property Value

Diamond? It follows any of your requirements!

Beryllium Oxide is the second after diamond. But BeO is carcinogenic and may cause chronic beryllium disease