Abstract—: The formation of metallic and carbide phases during the thermal decomposition of a mixture of the coordination compound [NiEn3]WO4 (En = ethylenediamine) and LiH in a He atmosphere has been studied by X-ray diffraction. The results demonstrate that heat treatment of the mixture at 410°C for 10 min leads to the formation of a Ni(Cx) interstitial solid solution based on the HCP Ni lattice and a W1 –xNix substitutional solid solution based on the BCC W lattice. Starting at 510°C, a Ni1 –xWx solid solution based on the FCC Ni lattice is also formed. The double carbide Ni2W4Cx appears at 660°C, and Ni6W6Cx forms at 860°C. Under similar conditions (700°C, He), the thermal decomposition of a mixture of NiWO4 and LiH leads to the formation of W and an FCC Ni1 –xWx (x ~ 0.12) solid solution.