The crystal structure of boron-doped superconducting $\mathrm{Mg}{\mathrm{C}}_{1-x}{}^{11}\mathrm{B}_x{\mathrm{Ni}}_3$, studied by powder neutron diffraction, is reported. The solubility limit of boron is determined to be approximately $x=0.16$. The unit cell expands from $a=3.81089\left(2\right)\mathrm{\AA }\text{to}3.81966\left(2\right)\mathrm{\AA }$ as $x$ increases from $x=0$ to $x=0.155$. Boron $\left({}^{11}\mathrm{B}\right)$ doping decreases $T_c$ with increasing $x$: from $7.09\mathrm{K}$ $(x=0)$ to $6.44\mathrm{K}$ $(x=0.155)$.

• Received 18 December 2004

DOI:https://doi.org/10.1103/PhysRevB.71.184512