Coloration of Pure and Doped Calcium Fluoride Crystals at 20°C and -190°C

Scouler, W. J.; Smakula, Alexander

doi:10.1103/physrev.120.1154

Cited by 87 publications

(26 citation statements)

References 15 publications

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“…The lattice parameters d and a calculated according to the XRD parameters are listed in Table 1, which presents that the lattice parameters have changed significantly contrasting with JCPDS standard card (35-0816), indicating that Li + and Na + ions incorporate into the CaF 2 crystal lattice [23] . The effective ionic radius of Na + is larger than Ca 2+ (r na =1.18 Å, r ca =1.12 Å), and the lattice parameter a of B was larger than pure calcium fluoride, the results are similar with the work done by Scouler [24] , the Na + ions occupied some positions of Ca 2+ ions and F  vacant lattice sites formed for electronic balance. But the ionic radius of Li + is much smaller than Ca 2+ (r Li =0.76 Å), if Li + ions replaced Ca 2+ and F  holes formed, the lattice parameter a should decrease, however the value a increased, disagreeing with the theory deduction, so it was interstitial solid solution for sample A.…”

Section: Resultssupporting

confidence: 85%

“…Liquid phase emerged in the sintering process of sample A, which induced faster and abnormal grain growth, as well as crystal growth preferential orientation indicated by the (111) predominant orientation of sample A's XRD patterns in Fig.4. The liquid phase accelerated the diffusion of sintering materials, and the diffusion was so fast that some volume of air was not removed out of the crystals, thus there are more residual inner-grain pores seen in sample A but not in sample B. the eutectic [24] of CaF 2 and NaF already emerged, which also accelerated the diffusion of sintering materials. But the liquid phase was so small and disappeared with the process of solid solution.…”

Section: Resultsmentioning

confidence: 92%

See 1 more Smart Citation

Effects of sintering additives on preparation of CaF2 transparent ceramics

Zhi

Mei

Zhou

et al. 2011

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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The effects of different sintering addictives on the preparation of CaF 2 transparent ceramics were studied. Transparent CaF 2 ceramics were fabricated by vacuum sintering and hot isostatic pressing (HIP) method, using CaF 2 nanopowders synthesized by chemical precipitation method as raw materials. The nanopowders and transparent ceramics were studied using X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and spectrophotometer. The experimental results indicated that the obtained nanopowders presented normal distribution with grain size about 30 nm; transmittance of CaF 2 transparent ceramics was 39% and 26% at 1100 nm for LiF and NaF as sintering addictives, respectively, with corresponding mean grain size 188 μm and 44 μm. Loss of transmission could be attributed to the residual closed porosity. Sintering mechanism was liquid-phase sintering at pre-stage, then solid-phase sintering at later stage, as well as solid solution of lithium ions and sodium ions in the CaF 2 lattice structure.

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Section: Resultssupporting

confidence: 85%

Section: Resultsmentioning

confidence: 92%

Effects of sintering additives on preparation of CaF2 transparent ceramics

Zhi

Mei

Zhou

et al. 2011

J. Wuhan Univ. Technol.-Mat. Sci. Edit.

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“…d similar spectrum for an yttrium doped crystal after X-irradiation was reported by Scouler and Smakula [4]. It should be noted that there is now a uv absorption similar t o that in the undoped crystal (cf.…”

Section: Resultssupporting

confidence: 59%

Dielectric and Optical Absorption Measurements on CaF₂ and CaF₂:Y

Caffyn

Goodfellow

Olymbios

et al. 1967

Physica Status Solidi (b)

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Crystals of oxygen free and oxygen contaminated CaF, were doped with yttrium. The dielectric loss of the unirradiated crystals was measured at 150 "C a t different frequencies and a shift of the peak in the curves was found with varying concentration of yttrium. In oxygen free crystals the peak was displaced to higher frequencies whilst with oxygen contaminated crystals the shift was to lower frequencies. The optical absorption spectra were taken a t room temperature before and after room temperature X-irradiation. The uv optical absorption that exists in oxygen contaminated crystals even before X-irradiation was found to decrease in yttrium doped crystals grown from oxygen contaminated material. It is proposed that the observed results could be explained on the assumption that one or more of the following associated defects are present in the crystals, namely: 1. an oxygen ion and fluorine ion vacancy, 2. an yttrium ion and an interstitial fluorine ion, 3. a n yttrium ion and a subst,itutional oxygen ion. The shift of the dielectric loss peak to lower frequencies for yttrium doped oxygen contaminated crystals is correlated with the reduct,ion of the uv optical absorption. It is suggested that possible explanation for this rednction is due to the formation of yttrium-oxygen dipoles. Thermal annealing of these crystals provides further confirmation of this suggestion.

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“…Why did the 580 nm band appear when the sample was exposed to a high-dose irradiation? The reasons could be as follows: As previously reported by Scouler [12], the 580 nm band very probably corresponds to electrons trapped in anion vacancies and, because of the presence of Na + ions, the 580 nm band shifts to 605 nm in NaF-doped CaF 2 crystals. Smakula and Messner [10] showed that the 580 nm band in electron-beam-colored CaF 2 crystals shifted to 600 nm with decreasing temperature to −190C.…”

Section: Discussionmentioning

confidence: 79%