Band-structure calculations were performed on Zr${\mathrm{Te}}_{5}$ to probe the puzzling behavior of the resistive anomaly observed in Zr${\mathrm{Te}}_{5}$ and Hf${\mathrm{Te}}_{5}$. This calculation shows that Zr${\mathrm{Te}}_{5}$ is a semimetal and that the carriers originate primarily from the tellurium $p$ orbitals. The nature of the bands is quite different from those in the structurally similar compound Nb${\mathrm{Se}}_{3}$, where the carriers are based on niobium $d$ orbitals.

Measurements of the nonlinear conductivity in Nb${\mathrm{Se}}_{3}$ resulting from the high-temperature charge-density wave (CDW) have been made. The results show that the electronic properties of Nb${\mathrm{Se}}_{3}$ in the temperature regime where only one CDW exists are qualitatively the same as those in the the region where two CDW's coexist. In both cases a threshold field for non-Ohmic conduction and quasiperiodic noise are observed. These results rule out mechanisms for noise production which rely on the coexistence of two CDW's, such as beat phenomena. Measurements of the temperature dependence of the two threshold fields show a separate depinning of each of the two CDW's at temperatures below 59 K. No evidence for a lock-in of the two threshold fields to a common value has been seen.

High-resolution x-ray scattering studies show a new charge-density wave (CDW) structure on warming through the commensurate-incommensurate transition in $2H$-Ta${\mathrm{Se}}_{2}$ at 93 K. In contrast to the fully incommensurate CDW structure seen on cooling, hexagonal symmetry is broken in the new phase and the triple-$\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$ CDW has one commensurate and two incommensurate wave vectors. At 112 K (warming) the CDW transforms to the fully incommensurate structure.

A detailed study has been made of interdiffusion in (GaAs)n(AlAs)m multilayer structures grown by molecular beam epitaxy. The subscripts n and m indicate that the structure is a repeating sequence of n monolayers of GaAs followed by m monolayers of AlAs. The time dependence of the Fourier components of the composition modulation at a constant annealing temperature was obtained by measuring the intensities of the superlattice satellites by x-ray diffraction. For a sample with (n,m) = (12,9) at a temperature of 860 °C, the data can be fit by a composition-dependent diffusion coefficient of the form D (C) =8.8×10−20 exp(αC) cm2/sec, where α=2.06 and C is the gallium concentration. The parameter α is proportional to the difference in the diffusion activation energy in GaAs and AlAs. An α of 2.06 at 860 °C corresponds to an energy difference of 0.201 eV. Calculations which assume vacancy diffusion via the arsenic sublattice give an energy difference of 0.25 eV in reasonable agreement with the experimental value. The average diffusion constant for a sample with (n,m) = (1.1,1.1) is 5.3×10−21 cm2/sec at T=800 °C. These results are in good agreement with those reported in the literature. In addition, a large growth anisotropy is observed in the (100) plane with a larger correlation length in the direction parallel to the dangling bonds on the As-rich surface of GaAs.

X-ray scattering studies of Nb${\\mathrm{Se}}_{3}$ show the formation of two independent, incommensurate charge-density waves (CDW) with wave vectors ${\\stackrel{\\ensuremath{\\rightarrow}}{\\mathrm{q}}}_{1}=(0, 0.243, 0)$ and ${\\stackrel{\\ensuremath{\\rightarrow}}{\\mathrm{q}}}_{2}=(0.5, 0.263, 0.5)$ at ${T}_{1}=144$ K and ${T}_{2}=59$ K, respectively. Electric fields that suppress the resistive anomaly associated with the lower-temperature CDW have no measurable effect on either the CDW amplitude or wave vector. The field required for suppression appears to scale roughly with the defect concentration as measured by the residual-resistance ratio. These results are consistent with the Fr\\ohlich sliding-CDW model with impurity pinning.