Chromium as resonant donor impurity in PbTe

We synthesize and perform structural, thermoelectric, magnetic, and (TeNMR)-Te-125 characterization measurements on chromium-doped PbTe. Te-125 NMR and magnetic measurements show that Pb1-xCrxTe is a solid solution up to x = 0.4 at.% and forms an n-type dilute paramagnetic semiconductor. The Cr level is resonant and pins the Fermi level about 100 meV into the conduction band at liquid nitrogen temperatures and below, but it moves into the gap as the temperature increases to 300 K. Te-125 NMR spectra exhibit a Knight shift that correlates well with Hall effect measurements and resolve peaks of Te near Cr. Magnetic behavior indicates that Cr exists mainly as Cr2+. No departure from the Pisarenko relation for PbTe is observed. Secondary Cr2Te3 and Cr3+delta Te4 phases are present in samples with x > 0.4%.