sentences:  They are usually carbon deficient and have nominal formulas TaCx and HfCx, with x = 0.7–1.0 for Ta and x = 0.56–1.0 for Hf.The same structure is also observed for at least some of their solid solutions.The density calculated from X-ray diffraction data is 13.6 g/cm3 for Ta0.5Hf0.5C.