| http://www.w3.org/ns/prov#value | - In AlN crystal grains constituting a sintered body, is contained: 150 ppm-0.5 wt. %, preferably at most 0.1 wt.%, of at least one rare earth element (as oxide thereof); at most 900 ppm, preferably at most 500 ppm of at least one metal impurity except rare earth elements; and preferably at least 0.5 wt. % of oxygen measured by an electron probe X-ray microanalyzer.
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