Single Crystalline Sapphire Research Articles

Phonon focusing in quartz and sapphire imaged by electron beam scanning

Anisotropic phonon propagation and phonon focusing in single-crystalline α-quartz and sapphire has been investigated using electron beam scanning for imaging the ballistic phonon propagation. The samples were circular disks of 20 mm diameter and 2.0 mm thickness. The phonons generated at the upper flat sample surface by the electron beam were detected with a small-size (43 μm×41μm) bolometer at the center of the opposite surface. The experiments were performed using a scanning electron microscope with a low-termperature stage. During electron irradiation of the upper sample surface the bottom of the sample was in direct contact with the liquid-He bath. For α-quartz, also time-resolved imaging of the phonon intensity has been performed in addition to imaging of the time-integrated bolometer signal. Our results agree remarkably well with calculations by Rosch and Weis.

The structure factor of liquid nickel at 1873K

The structure factor of liquid nickel at 1873K was measured by neutron diffraction using an orientated single-crystalline sapphire sample container. The effective spin quantum number has been found to be 0<or=S<or=0.3. The result is compared with the PY hard-core structure factor and the agreement is improved by an extension corresponding to an attractive part in the pair potential.

The Defect Structure of Unintentionally Doped α‐Al2O3 Crystals

Electrical conductivity and the ionic and electronic transference numbers were determined for two types of unintentionally doped single crystalline sapphire for current directions perpendicular to the r plane (1102). One was acceptor dominated and the other was initially donor (Hix) dominated, changing to acceptor domination after a prolonged anneal at 1600°C. The positions of the electronic energy levels of dominant impurities and the constants regulating the oxidation‐reduction of these impurities and of pure Al2O3 are determined. The latter shows a discrepancy with an expression reported previously.

THERMOLUMINESCENCE OF GOLDEN SAPPHIRE AND FUSED BORAX SEEDED WITH Ni, Mg, AND UO3

Thermoluminescence of golden sapphire (Al/sub 2/O/sub 3/ containing Ni and Mg impurities) was compared to a sample of soda boron oxide glass containing a small amount of nickel, then to a sample containing magnesium, and finally to a sample containing both nickel and magnesium. A comparison also was made of glow curves for various weight percents of UO/sub 3/ as the network modifier in the glass structure. Thermoluminescence glow curves were produced after gamma irradiation for samples of fused borax glass seeded with Ni, Mg, and UO/sub 3/. All of the thermoluminescence peaks were reproducible after successive irradiations and were found to lie in one of three ranges; 80 deg K, 168 plus or minus 5 deg K, and 228 plus or minus 5 deg K. After many irradiations at liquid nitrogen temperatures and annealing to room temperature, the sample containing only Ni showed an increase in the intensity for the 228 deg K peak. The glow curves for single crystalline golden sapphire showed characteristics different from the Ni and Mg seeded glass samples. The thermoluminescence peaks showed a decrease with cumulative and successive 30 min irradiations, and the peaks occurred at slightly increased temperatures. (P.C.H.)