| 1. |
- Andersson, Odd E., et al.
(författare)
-
A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite : Part IV: Basal plane resistivity
- 1995
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 10:7, s. 1653-1660
-
Tidskriftsartikel (refereegranskat)abstract
- Using an inductive technique, we have measured the in-plane resistivity rhoa of stages 2, 4, 5, and 8 SbCl5-GIC's versus temperature T and pressure p in the ranges 130–300 K and 0–0.85 GPa. The room temperature values of rhoa range from 4.0 µOcm for the stages 5 sample to 7.7 µOcm for the stage 8 sample. At all pressures, rhoa shows a metallic temperature dependence rhoa ~ Ta, with 1 < a < 2, but in contrast to the c-axis resistivity rhoc, it depends only very weakly on pressure and/or intercalate structural order. We show that the behavior observed is consistent with a band conduction model.
|
|
| 2. |
- Hultman, L, et al.
(författare)
-
Growth and electronic properties of epitaxial TiN thin films on 3C-SiC(001) and 6H-SiC(0001) substrates by reactive magnetron sputtering
- 1996
-
Ingår i: Journal of Materials Research. - 0884-2914. ; 11:10, s. 2458-2462
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N2 discharge at a substrate temperature of 700°C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001) ∥ 3C-SiC(001), and TiN[110] ∥ 3C-SiC[110], and TiN(111) ∥ 6H-SiC(0001) and TiN[110],[101] ∥ 6H-SiC[1210]. In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 × 10-3 Ω cm2 for a 6H-SiC substrate with an n-type doping of 5 × 1017 cm-3.
|
|
| 3. |
- Shen, Zhijian, et al.
(författare)
-
Effects of phase equilibrium on the oxidation behavior of rare-earth-doped α-sialon ceramics
- 1999
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 14:4, s. 1462-1470
-
Tidskriftsartikel (refereegranskat)abstract
- A series of rare-earth-(RE)doped α-sialons (RExSi12-4.5xAl4.5xO1.5xN16-1.5x, with X = 0.4 for RE = Nd, Sm, Yb, and x = 0.48 for RE = Y) were prepared and heat-treated in air at 1350 oC for 66-727 h (3-30 days), and the variation in composition and structure with time of the formed oxide scales and matrix materials were investigated. In the oxide scales of the Nd-, Sm-, and Y-containing samples a liquid was formed, apparently in (quasi-)equilibrium with the crystalline phases cristobalite and mullite, while only crystalline Yb2Si2O7, cristobalite, and mullite were observed in the Yb sample. Apparently, the liquid plays an important role in the oxidation process. In the depleted zone, located between the scale and the matrix, the liquid attacks the matrix phases, and a process takes place in which the originally formed phases dissolve and repricipitate as more oxygen-rich phases. In the Nd- and Sm-doped systems, where the α-sialon phase is inherently metastable at 1350 oC, an extensive α → β-sialon transformation takes place, creating still more liquid. As a consequence, the oxidation resistance of α-sialons containing Nd and Sm is much lower than those containing Y and, in particular, Yb.
|
|
| 4. |
- Sundqvist, Bertil, et al.
(författare)
-
A study of temperature and pressure-induced structural and electronic changes in SbCl5 intercalated graphite : Part III. Analysis of the T and p dependence of the c-axis resistivity
- 1995
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 10:2, s. 436-446
-
Tidskriftsartikel (refereegranskat)abstract
- We present experimental data for the c-axis electrical resistivity of SbCl5 intercalated graphite between 20 and 300 K. The data are analyzed together with our previous results for these and other samples [O. E. Andersson et al., J. Mater. Res. 7, 2989 (1992)]. Before the analysis, we correct the experimental data to constant volume, as assumed by theorists. We show that the correction factor is much larger for these materials than for normal metals. Although the original data showed significant nonlinearities with T, the corrected data are linear in T to within the experimental accuracy for low-stage compounds below the intercalate crystallization temperature. We compare our results with several models and conclude that both the temperature dependence, the pressure dependence, and the relative changes in the in-plane and c-axis resistivities associated with intercalate crystallization can be best described by a band conduction model.
|
|
| 5. |
- Swamy, V, et al.
(författare)
-
High-temperature powder x-ray diffraction of yttria to melting point
- 1999
-
Ingår i: JOURNAL OF MATERIALS RESEARCH. - : MATERIALS RESEARCH SOCIETY. - 0884-2914. ; 14:2, s. 456-459
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Powder x-ray diffraction data of yttria (Y2O3) were obtained from room temperature to melting point with the thin wire resistance heating technique. A solid-state phase transition was observed at 2512 +/- 25 K and melting of the high-temperature phase at
|
|
| 6. |
- Yakimova, R, et al.
(författare)
-
Silicon carbide grown by liquid phase epitaxy in microgravity
- 1998
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 13, s. 1812-1815
-
Tidskriftsartikel (refereegranskat)abstract
- 6H and 4H polytype silicon carbide (SiC) layers have been grown on ground and under microgravity conditions by liquid phase epitaxy (LPE) from a solution of SiC in Si-Se solvent at 1750 degrees C. The effects of gravity on the growth parameters and material characteristiques have been studied. The growth rate, Sc incorporation, and the structural defects are modified in reduced gravity conditions, while the polytype reproduction of the substrate is not affected. The results obtained are intriguing as to further experiments providing objects for carrier lifetime measurements.
|
|
| 7. |
- Yashar, PC, et al.
(författare)
-
Deposition and mechanical properties of polycrystalline Y2O3/ZrO2 superlattices
- 1999
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 14:9, s. 3614-3622
-
Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline Y2O3/ZrO2 superlattice thin films were deposited using opposed-cathode reactive magnetron sputtering. Pulsed direct-current power was used to eliminate arcing on the metallic targets. Radio-frequency power was applied to the substrates to achieve ion bombardment of the growing film. In order to reproducibly deposit at high rates in Ar-O-2 mixtures, the Y target voltage was used to indirectly feedback-control the O-2 partial pressure. Deposition rates as high as similar to 70% of the pure metal rates were achieved, typically 3.5 mu m/h. Superlattices with periods ranging from 2.6 to 95 nm were deposited. Y2O3 layer thicknesses were either 75% or 50% of the superlattice period. X-ray diffraction and transmission electron microscopy studies showed well-defined superlattice layers. The ZrO2 layers exhibited the high-temperature cubic-fluorite structure, which was epitaxially stabilized by the cubic Y2O3 layers, for thicknesses less than or equal to 7 nm. The equilibrium monoclinic structure was observed for thicker ZrO2 layers. Nanoindentation hardnesses ranged from 11.1 to 14.5 GPa with little dependence on period. The hardness results are discussed in terms of current superlattice hardening theories.
|
|
| 8. |
- Yun, S H, et al.
(författare)
-
Growth of a-axis-oriented HgBa2CaCu2Ox thin films by rapid quenching
- 1999
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 14:8, s. 3181-3184
-
Tidskriftsartikel (refereegranskat)abstract
- High-quality a-axis-oriented HgBa2CaCu2Ox superconducting thin films have been grown on (100) LaAlO3 substrates using a modified conventional method that contains a short annealing time of 5 min, rapid-quenching process, and an alternative encapsulated approach. We found that the preferred orientations of HgBa2CaCu2Ox thin films can be controlled by rapid quenching at specific temperatures: 800, 700, 600, and 500 degrees C. The films rapidly quenched in water from 700 degrees C during a cooling cycle showed predominantly a-axis orientation perpendicular to the film surface. Phase was confirmed by x-ray diffraction pole figures. The a-axis films exhibited a zero-resistance transition temperature >120 K, which is comparable to epitaxial c-axis-oriented films.
|
|
