Transport properties of binary phosphide AgP2 denoting high Hall mobility and low lattice thermal conductivity

Abstract

This study found that polycrystalline AgP2 shows intrinsic semiconducting electrical conductivity with Hall mobility of 51 cm2 V−1 s−1, which is as high as that of Mg2Si, and lattice thermal conductivity of 1.2 W K−1 m−1, which is as low as that of Bi2Te3. First-principles calculations theoretically indicate AgP2 as an intrinsic semiconductor, and indicate the estimated carrier relaxation time τ as 3.3 fs, which is long for a polycrystalline material. Moreover, the effective mass of hole m* is approximately 0.11 times that of free electrons. These results indicate that long τ and light m* of the carrier are the origins of the high experimentally obtained Hall mobility. Phonon calculations indicate that the Ag atoms in AgP2 exhibit highly anharmonic phonon modes with mode Grüneisen parameters of more than 2 in the 50–100 cm−1 low-frequency range. The large anharmonic vibrations of the Ag atoms reduce the phonon mean free path. Moreover, the lattice thermal conductivity was found, experimentally and theoretically, to be as low as approx. 1.2 W K−1 m−1 at room temperature by phonon–phonon and grain-boundary scattering.