Chromium as resonant donor impurity in PbTe

We synthesize and perform structural, thermoelectric, magnetic, and ¹²⁵Te NMR characterization measurements on chromium-doped PbTe. ¹²⁵Te NMR and magnetic measurements show that Pb_1-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. ¹²⁵Te 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 Cr_3+δTe₄ phases are present in samples with x > 0.4$%$.