Charge-density wave stacking order in1T−Ta1−xZrxSe2: Interlayer interactions and impurity (Zr) effects

Ordering of the commensurate charge-density waves (CDWs) from layer to layer in $1T-{\mathrm{Ta}}_{1-x}{\mathrm{Zr}}_x{\mathrm{Se}}_2$ is observed by neutron diffraction to give superlattice Bragg peaks at $\frac{2c^{*}}{13}$, $\frac{5c^{*}}{13}$, and $\frac{6c^{*}}{13}$ for $x\le 0.015$. With larger Zr concentration ($x=0.03\mathrm{}$), a broad peak (full width at half maximum of $0.1c^{*}$ centered at $\frac{c^{*}}{3}$ is found. Nearest- and next-nearest-layer interactions are required to explain the implied stacking sequences in the pure limit. As impurities are added, the random potential dominates the next-nearest-layer interaction and a disordered CDW stacking structure develops. A simple model of this disorder is presented which accurately fits the observed scattering profiles.