Abstract: A process for preparing a heat-treated body from a material (preferably a dielectric ceramic) that does not couple well with microwaves while nevertheless using microwave energy for the heating step. The process involves the use of a microwave susceptor (i.e. a material that couples well with microwaves) as a means for generating heat in the material. To avoid contamination of the final product, a susceptor is chosen which is converted, during the heating step, to a substance which is substantially the same as the material itself, both the susceptor and the material are converted to the same desired final product, or the material is converted to a substance substantially the same as the susceptor. The resulting substantially pure heat-treated (and preferably sintered) bodies can be used for a variety of purposes, e.g. as substrates for micro-electronic devices. The process can also be used for joining bodies of non-susceptor materials without contaminating the resulting joint.