  By determining the lattice parameters as a function of temperature of the
hexagonal van der Waals ferromagnet Fe$_{2.92(1)}$Ge$_{1.02(3)}$Te$_2$ we
obtain the temperature dependence of the spontaneous in-plane magnetostriction
in the ferromagnetic and the linear thermal expansion coefficients in the
paramagnetic state. The spontaneous magnetostriction is clearly seen in the
temperature dependence of the in-plane lattice parameter $a(T)$, but less well
pronounced perpendicular to the planes along $c$. Below $T_{\rm C}$ the
spontaneous magnetostriction follows the square of the magnetization and leads
to an expansion of the hexagonal layers. Extrapolating to $T\rightarrow$ 0~K we
obtain a spontaneous in-plane saturation magnetostriction of $\lambda_{{\rm
sp},a}(T \rightarrow 0) \approx-220 ~\times~10^{-6}$. In the paramagnetic state
the linear thermal expansion coefficients amount to
13.9(1)$\times$10$^{-6}$~K$^{-1}$ and to 23.2(2)$\times$10$^{-6}$~K$^{-1}$ for
the in-plane and out-of-plane direction, respectively, indicating a linear
volume thermal expansion coefficient of 50.8(4)$\times$10$^{-6}$K$^{-1}$ which
we use to estimate the volume thermal expansion contribution to the heat
capacity determined at constant pressure. A Sommerfeld-type linear term in the
low-temperature heat capacities can be quantitatively ascribed to 2dim
ferromagnetic magnon excitations.
