Cu(x)UTe3: 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.

Abstract

The ternary phase, Cu(x)UTe3 (x = 0.25 and 0.33), was synthesized from a 3/1/4 mixture of Cu/U/Te that was heated to 800 degrees C for 6 days and cooled at a rate of -4 degrees C x h(-1). It adopts the monoclinic space group P2(1)/m with a = 6.0838(12) A, b = 4.2140(8) A, c = 10.361(2) A, beta = 98.83(3) degrees, and V = 262.47(9) A3 (for x approximately 0.25). The structure is built from UTe3 layers of ZrSe3-type that are connected in the [001] direction by Cu atoms. The Cu atoms stabilize alpha-UTe3 by inserting between the layers. Cu(x)UTe3 can be prepared rationally via a soft chemistry route by reaction of Cu with alpha-UTe3. The structural analysis suggests the presence of straight chains of Te atoms ( approximately 3.0 A apart) along the a-axis but this is an artifact as shown by electron diffraction studies of Cu(x)UTe3 that indicate the existence of a supercell 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 A. Charge transport measurements suggest a narrow gap semiconductor but they also indicate anomalous behavior as a function of temperature with a n-type to p-type transition at approximately 40 K.