The design and construction of a specialised sample cell for the simultaneous investigation of electron-transport and structural properties by powder neutron diffraction in the temperature range1.5 ≤ T /K ≤ 300 is described. This cell has been used to investigate the structural origin of anomalies in the transport properties of the pseudo-one-dimensional ternary sulfide TlCu7–δS4 (δ = 0.15). The data reveal an anomaly in ρ(T) observed at 255 K, which is associated with a phase change involving a change in symmetry from I4/m to P4/n on cooling. This corresponds to a doubling of the crystallographic c axis and is evidenced by the splitting of a strong reflection at d = 2.28 Å and the appearance of additional peaks in the low-temperature diffraction data. A lower temperature ρ(T) anomaly at 205 K is related to subtle structural distortions involving chains of edge-shared Cu4 tetrahedra.