Introduction

Abstract

The availability of isotopically pure crystals with low carrier and impurity concentrations has allowed the investigation of isotopic effects on lattice dynamic and electronic properties of solids in the last three decades [23]. Due to zero-point motion, the atoms in a solid feel the anharmonicity [28] of the interatomic potential, even at low temperatures. Therefore, the lattice parameters of two chemically identical crystals formed by different isotopes do not coincide [23,106,428]; heavier isotopes have smaller zero-point delocalization (as expected in a harmonic approximation) and smaller lattice parameters (an anharmonic effect). Moreover, phonon-related properties such as thermal conductivity, thermal expansion, and melting temperature are expected to depend on isotope mass.