CuxUTe3: Stabilization of UTe3 in the ZrSe3 structure type via copper insertion. The artifact of Te-Te chains and evidence for distortions due to long range modulations

The ternary phase, CuxUTe3 (x = 0.25 and 0.33), was synthesized from a 3/1/ 4 mixture of Cu/U/Te that was heated to 800 degreesC for 6 days and cooled at a rate of -4 degreesC h(-1). It adopts the monoclinic space group P2(1)/ m with a = 6.0838(12) Angstrom, b = 4.2140(8) Angstrom, c = 10.361(2) Angst rom,beta = 98.83(3)degrees, and V = 262.47(9) Angstrom (3) (for x similar t o 0.25). The structure is built from UTe3 layers of ZrSe3-type that are con nected in the [001] direction by Cu atoms. The Cu atoms stabilize alpha -UT e3 by inserting between the layers. CuxUTe3 can be prepared rationally via a soft chemistry route by reaction of Cu with alpha -UTe3. The structural a nalysis suggests the presence of straight chains of Te atoms (similar to3.0 Angstrom apart) along the a-axis but this is an artifact as shown by elect ron diffraction studies of CuxUTe3 that indicate the existence of a superce ll along the a-axis. Pair distribution function analysis (PDF) was used to show that the Te-Te chains contain Te-Te dimers at 2.74 Angstrom. Charge tr ansport measurements suggest a narrow gap semiconductor but they also indic ate anomalous behavior as a function of temperature with a n-type to p-type transition at similar to 40 K.