A process is provided for forming a material comprising an M3X1Z2 phase comprising the steps of: (a) providing a mixture of (i) at least one transition metal species, (ii) at least one co-metal species selected from the group consisting of aluminum species, germanium species and silicon species, and (iii) at least one non-metal species selected from the group consisting of boron species, carbon species and nitrogen species; (b) heating said mixture to a temperature of about 1000° C. to about 1800° C., in an atmosphere within a substantially enclosed heating zone, for a time sufficient to form said M3X1Z2 phase; wherein the atmosphere has an O2 partial pressure of no greater than about 1×10−6 atm. The process provides a substantially single phase material comprising very little MZx-phase. A process for preparing a dense, substantially single-phase M3X1Z2 phase workpiece includes providing a highly-pure M3X1Z2-phase powder pre-form and sintering said pre-form at a temperature of about 1000° C. to about 1800° C., in an atmosphere within a substantially enclosed heating zone, for a time sufficient to form a dense, substantially single-phase, M3X1Z2-phase workpiece; wherein the atmosphere has an O2 partial pressure of no greater than about 1×10−6 atm.