Praseodymium ditelluride is an inorganic compound of praseodymium and tellurium with the formula PrTe2. It is a layered rare-earth telluride in which praseodymium is essentially trivalent and the tellurium atoms form several types of polyanionic Te–Te units. It exhibits strongly two-dimensional metallic electronic behaviour and a charge-density wave state.
Preparation Single crystals of PrTe2 can be prepared by chemical vapor transport from praseodymium and tellurium using small amounts of iodine as a transport agent:
Pr + 2 Te → PrTe2
Properties Structure PrTe2 crystallizes in the tetragonal crystal system, space group P4, with lattice parameters a = 8.9680(5) Å and c = 18.119(1) Å and 16 formula units per unit cell. Its structure is a 2 × 2 × 2 superstructure of the simpler anti-Fe2As-type rare-earth ditelluride structure. It is isotypic with CeTe2, whereas LaTe2 adopts a related monoclinically distorted superstructure. The structure consists of alternating praseodymium–tellurium slabs and planar polytelluride layers. The latter contain several distinct Te–Te bonding motifs, including Te2 dumbbells arranged in a herringbone pattern and both approximately square and rectangular Te4 units. These different arrangements occur in different tellurium layers along the crystallographic c direction and account for the doubling of the superstructure relative to that found in LaTe2. Diffraction data indicate that the different polytelluride arrangements can occur as microdomains. The bonding is consistent with essentially Pr3+, while the tellurium sublattice carries the remaining negative charge through Te–Te bonded polyanions rather than consisting entirely of isolated Te2− ions.
Electronic properties PrTe2 is metallic. Photoemission measurements show a clear Fermi edge and electronic states crossing the Fermi level. Angle-resolved photoemission spectroscopy shows very weak dispersion perpendicular to the tellurium sheets, demonstrating that the electronic structure is predominantly two-dimensional. PrTe2 forms a charge-density-wave state associated primarily with the partially filled Te 5p bands of the planar tellurium sheets. The charge-density wave reconstructs the Fermi surface but does not completely gap it, so the material remains metallic. More recent X-ray absorption and photoemission measurements confirm that praseodymium is close to the +3 oxidation state. The Pr 4f electrons do not directly form the charge-density wave, although hybridization between Pr 4f and Te 5p states may influence it indirectly.
Magnetic properties PrTe2 is strongly magnetically anisotropic as a result of the crystalline electric field acting on Pr3+. In contrast to several related rare-earth ditellurides, PrTe2 shows no clear magnetic-ordering transition in measurements down to approximately 1.5 K. Specific-heat measurements between 1.5 and 200 K likewise found no sharp anomaly attributable to magnetic ordering in PrTe2.
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