Insulator−Metal and Structural Phase Phenomena in KxBa1-xCoS2 (x < 0.07)

Abstract

KxBa1-xCoS2 was synthesized by a new technique using a closed vitreous carbon crucible. Single crystals prepared from materials of nominal composition x = 0.2 were found to have only modest substitution levels (x ≈ 0.07) by microprobe and X-ray analysis. The substituted compounds crystallize in P4/nmm, a = 4.557(1), c = 8.957(2), R1 = 2.03%, and wR2 = 4.20%, as determined by single-crystal X-ray diffraction. Measurement of electrical resistivity by the van der Pauw method reveals a phase transition with hysteresis at about 170 K for cooling and 210 K upon warming, with semiconducting behavior above (ρ ≈ 10-2 Ω cm) and metallic-like behavior (ρ ≈ 10-3 Ω cm) below the transition. Magnetic susceptibility data show a second-order transition around 270 K, along with a first-order transition around 150−200 K that displays significant hysteresis. The transition at 270 K is probably due to the onset of antiferromagnetic order, whereas the transition at lower temperatures is associated with structural modification...