Tc Carbide and New Orthorhombic Tc Metal Phase

Abstract

Tc metal and metal-like carbide phases are revisited with special attention given to Tc-rich phases in the view of prospective nuclear fuel utilization and alternative transmutation targets fabrication. A new Tc-metal phase has been found and new softer conditions for the Tc carbide formation were observed. The unit cell parameters of a new orthorhombic Tc metal were a = 2.805(4), b = 4.958(8), c = 4.474(5)•ð (V/z = 15.55 •ð) for Tc-C with 1.38 wt.% C and a = 2.815(4), b = 4.963(8), c = 4.482(5) •ð (V/z = 15.65 A) for Tc-C with 1.96 wt.% C.

First-principles investigation of technetium carbides and nitrides

“…Nevertheless, for TcC and TcN in the NaCl phase, because negative C 44 ͑−61 and −178 GPa͒ will violate the requirement of positive strain energy, they are elastically unstable in contrast to the experimental observations of cubic NaCl phase. 26,28 There are two possible origins of this disagreement. Our calculation assumes stoichiometric TcC and TcN, while real samples contain C or N deficiency.…”

“…In 1962, Trzebiatowski and Rudzinski 26 first synthesized Tc carbide and claimed that Tc carbide forms the hexagonal structure with 1 wt % C and the fcc structure with 1.4-9 wt % C. Nevertheless, Giorgi and Szklarz 27 reported that Tc carbide was completely resolved as a bcc phase by an x-ray diffraction pattern, although its lattice parameter of 3.985Ϯ 0.002 Å is in agreement with that of the above fcc structure ͑3.982 Å͒. The synthesis of Tc-C has been also realized by German et al 28 in high-temperature vacuum furnace. According to German et al, 28 the structure of Tc-C system also depends on the carbon content and the temperature of preparation, and cubic fcc and orthorhombic structures have been obtained.…”

“…The synthesis of Tc-C has been also realized by German et al 28 in high-temperature vacuum furnace. According to German et al, 28 the structure of Tc-C system also depends on the carbon content and the temperature of preparation, and cubic fcc and orthorhombic structures have been obtained. Moreover, the fcc Tc carbide phase is defective in carbon and a range of Tc:C atomic ratio is from 1:1 to 5:1.…”

Debye temperature, thermal expansion, and heat capacity of TcC up to 100GPa

“…Nevertheless, Giorgi and Szklarz [14] reported that Tc carbide was completely resolved as a bcc phase by an X-ray diffraction pattern, although its lattice parameter of 3.985 AE 0.002 Å is in agreement with that of the above fcc structure (3.982 Å). In recently, the X-ray diffraction study by German et al [15] had proved the formation of cubic NaCl phase with a = 3.982 Å (Fm3m) in the interval of Tc:C ratios from 1:1 to 5:1, and the cubic Tc carbide phase was observed already at T = 800 C indicating that the conditions for its preparation could be much softer compared to that reported in [13], although this structure is elastically unstable because c 44 < 0 violates the requirement of positive strain energy from the point of the elastic constant calculations by Liang et al [12].…”

Phase transition, elastic and thermodynamical properties of TcC under high pressure from first-principles calculations

“…In addition, Tc carbides appear to have especially surprising importance in the fields of nuclear waste management and nuclear medicine [8,9]. Therefore, there is great interest for physicists in experimental [8][9][10][11][12] and theoretical investigations [13,14,25] of technetium carbides.…”