Superconductivity in Medium-Entropy Alloys: Nb₂TiW and Nb₂TiMo

Abstract This paper describes the synthesis and characterization of Nb 2 TiW and Nb 2 TiMo medium-entropy alloys (MEAs). The Nb 2 TiW and Nb 2 TiMo MEAs were successfully synthesized using the arc-melting method. Their structures and superconducting properties were investigated through detailed characterization using X-ray diffraction (XRD), resistivity, magnetization, and specific heat measurements. The XRD results confirmed that the obtained Nb 2 TiW and Nb 2 TiMo compounds have the same body-centered cubic (BCC) structure and crystallized in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>I</mml:mi> <mml:mi>m</mml:mi> <mml:mover accent="true"> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>m</mml:mi> </mml:mrow> </mml:math> space group (number 229). Experimental results showed that the superconducting transition temperatures ( T c s) of Nb 2 TiW and Nb 2 TiMo are approximately 4.86 and 3.22 K, respectively. The upper and lower critical fields of Nb 2 TiW are 3.52(2) T and 53.36(2) Oe, respectively, and those of Nb 2 TiMo are 2.11(2) T and 68.23(3) Oe, respectively. First-principles calculations revealed that the d electrons of Nb, Ti, and Mo or W are the dominant contributors to the density of states near the Fermi level. Specific heat measurement results indicated that Nb 2 TiW and Nb 2 TiMo exhibit BCS full-gap s -wave superconductivity.