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High pressure phase of LiGaO2
Vol. 3, No. 7
ABSTRACTS OF PAPERS TO APPEAR Di J. PjIYS. CHEM. SOLIDS
the radiation loss from the sample was balanced by use of an electronically controlled temperature distribution along the radiation shield, (ReceIved 21 September 1964) (RevIsed 3 February 1965) 16. THE EFFECT OF THE LATTICE ON THE OPTICAL ABSORPTION BAND WIDTH AN]) THE RAMAN EFFECT OF THE U-CENTRE. C. T. Bennett (Laboratolre de Spectroscopie et d’Optique do Corps Solide, Institut de Physique, Université de Strasbourg, France). A calculation of the U-centre in sodium chloride is presented using a consistent configuration coordinate model and taking into account the motion of the rest of the lattice. The width of the absorption band is calculated as a function of temperature, and used as a test of the model; the agreement is found to be about 10 per cent. The Raman effect of this centre is also calculated and the type of spectrum to be expected is shown in Fig. 4 of the paper. (Received 27 November 1964) (Revised 3 February 1965) 17. PHONONS IN CRYSTALLINE SOLIDS AND DILUTE BOSE GASES. A. Bardasis, David S. Falk and David A. Simkin(University of Maryland, College Park, Maryland, U.S.A.). Phonons in a crystalline solid and a dilute Bose gas are treated from a uniform point of view. In each of the cases, the potential is expanded about ionic (or atomic) “equilibrium” positions, with the important difference that in the gaseous state these positions are allowed to move. This motion leads to an additional term in the kinetic energy part of the gas Ilamiltonian, resulting in a dispersion relation for long wavelength density fluctuations identical to that obtamed by Bogoliubov. The usual lattice phonon spectrum is also reproduced. The limitations of the viewpoint when applied to liquids and Fermi gases are discussed. (Received 14 January 1965) (Revised 8 February 1965) 18. MECHANISM OF THE PRECIPITATION OF THE SPINEL FROM MgO-A1203 SOLID SOLUTIONS.
lxiii
V. S. Stubican and Ruituin Roy (Department of Ceramic Technology and Materials Research laboratory, The Pennsylvania State University, University Park, Pa., U. S. A.). The recently reported crystalline solubility of A1203 In MgO was confirmed. Unit cell dimensions and densities were measured ladependently and the existence of a predominant cation-vacancy model established for these crystalline solutions. The precipitation of the spinel was effected in the air at 1350°Cand 1100°Cand studied by quantitative X-ray dlffraction. The precipitation is a diffusion controlled process and the equation y= 1
-
exp [ (~)‘~] -
fits the experimental results for y = 0.05 0.95. The exponent n was found to be very close to 3/2, suggestIng that under the experimental conditions the growing particles were approximately spherical. -
Electron probe investigations showed that the preferred sites for the nucleation and the precipitation of spinel were the grain boundaries and intergranular voids. (Received 13 October 1964) (Revised 8 February 1965) 19. HIGH PRESSURE PHASE OF LiGaO. M. Marezio and J. P. Remelka (Be Telephone Laboratories, Inc., Murray Hill, New Jersey, U.S.A.). The crystal structure of a-LiGaO2 has been determined from powder data. This new phase is frigonal, space group R~m,with 3 molecules in a hexagonal cell of dimensions a = 2.9113 * 0.0003 A. It is isostructural with NaBF~. The catlons, lithium and gallium, are in 3(a)’and 3(b) positions respectively, while the oxygen atoms are in the 6(c) position with z = 0.242. Every atom is octahedrally coordinated and the structural arrangement is that of a NaC1-llke structure. The interatomic distances are Ga-O = 2.OOA, Li-O = 2. 14A. The dimorphism of LiGaO2 is discussed 3O that this is a unique case among and it Is shown the A~iB” 2compounds. The room temperature and pressure modIfication, 8, has a wurtzite-IIke structure and the high pressure modification, a, has a NaC1-like structure. (Received 8 February 1965)
ABSTRACTS OF PAPERS TO APPEAR Di J. PjIYS. CHEM. SOLIDS
the radiation loss from the sample was balanced by use of an electronically controlled temperature distribution along the radiation shield, (ReceIved 21 September 1964) (RevIsed 3 February 1965) 16. THE EFFECT OF THE LATTICE ON THE OPTICAL ABSORPTION BAND WIDTH AN]) THE RAMAN EFFECT OF THE U-CENTRE. C. T. Bennett (Laboratolre de Spectroscopie et d’Optique do Corps Solide, Institut de Physique, Université de Strasbourg, France). A calculation of the U-centre in sodium chloride is presented using a consistent configuration coordinate model and taking into account the motion of the rest of the lattice. The width of the absorption band is calculated as a function of temperature, and used as a test of the model; the agreement is found to be about 10 per cent. The Raman effect of this centre is also calculated and the type of spectrum to be expected is shown in Fig. 4 of the paper. (Received 27 November 1964) (Revised 3 February 1965) 17. PHONONS IN CRYSTALLINE SOLIDS AND DILUTE BOSE GASES. A. Bardasis, David S. Falk and David A. Simkin(University of Maryland, College Park, Maryland, U.S.A.). Phonons in a crystalline solid and a dilute Bose gas are treated from a uniform point of view. In each of the cases, the potential is expanded about ionic (or atomic) “equilibrium” positions, with the important difference that in the gaseous state these positions are allowed to move. This motion leads to an additional term in the kinetic energy part of the gas Ilamiltonian, resulting in a dispersion relation for long wavelength density fluctuations identical to that obtamed by Bogoliubov. The usual lattice phonon spectrum is also reproduced. The limitations of the viewpoint when applied to liquids and Fermi gases are discussed. (Received 14 January 1965) (Revised 8 February 1965) 18. MECHANISM OF THE PRECIPITATION OF THE SPINEL FROM MgO-A1203 SOLID SOLUTIONS.
lxiii
V. S. Stubican and Ruituin Roy (Department of Ceramic Technology and Materials Research laboratory, The Pennsylvania State University, University Park, Pa., U. S. A.). The recently reported crystalline solubility of A1203 In MgO was confirmed. Unit cell dimensions and densities were measured ladependently and the existence of a predominant cation-vacancy model established for these crystalline solutions. The precipitation of the spinel was effected in the air at 1350°Cand 1100°Cand studied by quantitative X-ray dlffraction. The precipitation is a diffusion controlled process and the equation y= 1
-
exp [ (~)‘~] -
fits the experimental results for y = 0.05 0.95. The exponent n was found to be very close to 3/2, suggestIng that under the experimental conditions the growing particles were approximately spherical. -
Electron probe investigations showed that the preferred sites for the nucleation and the precipitation of spinel were the grain boundaries and intergranular voids. (Received 13 October 1964) (Revised 8 February 1965) 19. HIGH PRESSURE PHASE OF LiGaO. M. Marezio and J. P. Remelka (Be Telephone Laboratories, Inc., Murray Hill, New Jersey, U.S.A.). The crystal structure of a-LiGaO2 has been determined from powder data. This new phase is frigonal, space group R~m,with 3 molecules in a hexagonal cell of dimensions a = 2.9113 * 0.0003 A. It is isostructural with NaBF~. The catlons, lithium and gallium, are in 3(a)’and 3(b) positions respectively, while the oxygen atoms are in the 6(c) position with z = 0.242. Every atom is octahedrally coordinated and the structural arrangement is that of a NaC1-llke structure. The interatomic distances are Ga-O = 2.OOA, Li-O = 2. 14A. The dimorphism of LiGaO2 is discussed 3O that this is a unique case among and it Is shown the A~iB” 2compounds. The room temperature and pressure modIfication, 8, has a wurtzite-IIke structure and the high pressure modification, a, has a NaC1-like structure. (Received 8 February 1965)