Herbert Engstrom

Infrared spectra of hydrogen isotopes in potassium tantalate

The spectroscopic constants of hydroxyl ions formed from hydrogen, deuterium, and tritium in a potassium tantalate (KTaO3) host have been determined. These isotopes were found to diffuse readily either into or out of KTaO3 single crystals. At T=77 K the infrared absorption band due to the OH−, OD−, or OT− stretching vibration is extremely narrow (i.e., ∼1.0, 0.8, and 0.7 cm−1, respectively). These results indicate that the interaction between the hydroxyl ions and the surrounding lattice is very weak. The optical properties of hydroxyl ions and the characteristic features of hydrogen diffusion in KTaO3 are compared with those determined previously for aluminum oxide (Al2O3) and rutile (TiO2).

Infrared reflectivity and transmissivity of boron‐implanted, laser‐annealed silicon

Analysis of the infrared reflectance and transmittance of boron‐implanted, laser‐annealed silicon shows that the Drude theory of free hole scattering provides a good description of the optical properties of these materials up to the highest doping levels obtainable. It was found that (1) the relaxation time (∼7×10−15 s) was independent of the implant dose, and (2) the boron concentration affecting the optical properties varies essentially linearly with implant dose.

Ionic conductivity of sodium beta″-alumina

Abstract Measurements of the electrical conductivity of Na s″-alumina show that the low-temperature activation energies are 0.3337 ± 0.0055 eV for MgO stabilized crystals grown at 1700°C, 0.275 ± 0.015 eV for crystals with the same starting composition position grown at 1650°C, and 0.1716 ± 0.0093 eV for crystals stabilized with ZnO and grown at 1700°C. The conductivities of almost all crystals at 500°C were found to be 1.3 ± 0.6 Ω−1 cm−1. In addition to the growth conditions, the presence of a dc electric field, the type of electrode material, the type of conducting ion, and the concentration of stabilizing ion are important in determining the electrical conductivity. These factors are believed to affect the nature of the ordering of vacancies in the s″-aluminas, leading to variations in the activation energy.

Non-Debye capacitance in single-crystal sodium beta-alumina☆

Abstract A recently proposed theory of non-Debye capacitance in solids is applied to complex impedance measurements of Na β-alumina. The results show conclusively that this material is a non-Debye solid whose admittance has a frequency exponent, n, of approximately 0.8 at room temperature. Values of the conductivity, susceptibility coefficient, and frequency exponent, as functions of temperature for 25°C≤T≤500°C are presented.

Composition, ion-ion correlations and conductivity of beta″-alumina☆

Abstract It is concluded from conductivity and diffuse x-ray scattering measurements on Mg stabilized Na and K β″-alumina single crystals that higher activation energies are associated with greater ordering of mobile ions on a superlattice. Similar measurements on Zn stabilized Naβ″ with a higher vacancy concentration suggest that the low temperature conductivity is mainly determined by the fraction of vacancies that are not ordered. The rapid decrease observed in the Raman intensity of the 144 cm −1 Na + mode with increasing temperature is attributed to fluctuations caused by thermal excitation of the low energy mode at 32 cm −1 .

Effect of H2O on the Ionic conductivity of sodium beta-alumina

Abstract The effect of water molecules on the ionic conductivity of sodium betaalumina single crystals was investigated. Water molecules intercalated in the conducting plane lower than the conductivity by as much as a factor of two.

Infrared absorption and Raman scattering from H2O in Na1−xLix beta aluminas

Abstract Infrared and Raman spectra of Na 1− x Li x beta-alumina single crystals (0⩽×⩽0.9) show bands in the 3000 to 3600 cm −1 region due to vibrations of H 2 O molecules located in the conducting plane. Hydration of Naβ-Al 2 O 3 occurs on exposure to water vapor while hydration of Na 1− x Li x β-Al 2 O 3 occurs primarily during ion exchange. The extent of hydration and stability of these hydrates increases with increasing Li + concentration. Based on a simple model, the completely hydrated state of pure lithium beta-alumina is represented by Li 2.3 O·11Al 2 ) 3 ·5.4H 2 O.

Raman scattering from mobile cations in sodium, potassium and silver beta”-aluminas

Abstract Raman scattering from vibrations of mobile cations in single crystal Na, K, and Agβ”-aluminas has been measured. The frequency of a band near 33 cm-1 is believed to correspond to the attempt frequency for sodium conduction. The frequencies calculated from a defect model are in good agreement with the observed spectra.

Raman scattering from boron‐implanted laser‐annealed silicon

Measurements of the line shape of the silicon optic mode in boron‐implanted ruby‐laser‐annealed silicon were analyzed assuming a Fano‐type interaction between the discrete optic mode and the continuous valence band states. The results yielded a utilization coefficient of 0.89±0.09 for the boron impurities. Measurements of the ratio of the intensity of the boron local mode to that of the silicon optic mode as a function of excitation wavelength are consistent with the conclusion of other workers that laser annealing is more effective than thermal annealing in reducing lattice damage.

Raman scattering from NH4+ and ND4+ in beta‐alumina

Polarized Raman spectra in the internal and external mode region of NH4+ and ND4+ ions in beta‐alumina have been measured. The forms of the scattering tensors for the internal modes are calculated taking into account the disordered distribution of ions on the crystallographic sites and treating each ion as an independent scattering center. The results of the analysis suggest that the ammonium ions occupy three nonequivalent sites in beta‐alumina. Model calculations indicate that the ions prefer the Beevers–Ross and midoxygen sites with the C2 axes of the ions located in the conducting plane. The librational modes of NH4+ and ND4+ evidently occur in the region from 200 to 450 cm−1, but overlap with phonons of the host lattice precludes positive identification. The in‐plane and out‐of‐plane translational modes are identified in the region between 100 and 200 cm−1.