Niobium films (120 nm thick) deposited by electron-beam evaporation were implanted near 5 K with 100 keV N(,2)('+) ions to maximum fluences of 4 to 7 x 10('17) N/cm('2). STEM diffraction patterns showed a structural phase transformation from the initial Nb lattice with 110 fiber texture (bcc, a(,o) = 3.30 (ANGSTROM)) to randomly oriented (delta)-NbN (fcc, a(,o) = 4.35-4.39 (ANGSTROM)), via an intermediate, highly disordered Nb-(interstitial N) structure (bcc, maximum a(,o) = 3.42 (ANGSTROM)). Decreases in transition temperature T(,c) from 9 K to a minimum of 3 K, and rapid linear increases in residual resistivity (rho)(,10), were observed to fluences of 1.0-1.5 x 10('17) N/cm('2), and were attributed to the accumulation of radiation-induced defects. Continued implantation resulted in (delta)-NbN formation and T(,c) increases to maximum values of 9-10 K which were achieved at fluences from 3.5 to 5.0 x 10('17) N/cm('2), corresponding to average substoichiometric N/Nb ratios of 0.52-0.75, at which point the phase transformation was complete. The (delta)-NbN formation was accompanied by significant lattice reordering and grain growth. At higher fluences, gradual T(,c) declines (by 1-2 K), and the sharp rises in (rho)(,10), were observed, possibly due to film sputtering. Large reductions in flux pinning force density F(,P) to fluences which produced minimum T(,c) values (about 1 x 10('17) N/cm('2)) were attributed to the destruction of strong grain boundary pinning centers by the ion bombardment. Substantial recovery of F(,P) to levels below the initial values occurred at higher fluences, probably due to the grain recrystallization and larger upper critical fields H(,c2) (H(,c2)(O) (TURN) 75-110 kOe) of the (delta)-NbN phase. / Source: Dissertation Abstracts International, Volume: 46-04, Section: B, page: 1226. / Thesis (Ph.D.)--The Florida State University, 1985.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75576 |
| Contributors | JOHNSON, JEFFREY P., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 132 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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