Thermal expansion of crystals of lithium isotopes

The parameters of interatomic interaction in crystals of isotopes of lithium $^7\text{Li}$ and $^6\text{Li}$ are determined for both the minimal and maximal values of Debye temperature. These parameters and the Debye crystal model are used to calculate the temperature dependences of the coefficient of thermal expansion (CTE) and of the lattice parameter from $0$ K to the melting temperature of these crystals. It is demonstrated that the temperature dependences of CTE for crystals of $^7\text{Li}$ and $^6\text{Li}$ intersect at temperature $T_x = 230$–$300$ K so that, under conditions of melting, the CTE for crystal of light isotope is higher than that for crystal of heavy isotope of lithium.