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  • 1
    Electronic Resource
    Electronic Resource
    Positron Annihilation Lifetime Spectroscopy of Air-Fired Ca(1−x)(La)xTiO3 Perovskites (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In polycrystalline air-fired perovskites of Ca(1−x)(La)xTiO3 stoichiometry (x=0.00–0.15), the positron annihilation lifetime increased monotonically with x, and showed an ∼40% increase of the lifetime at x∼0.1, at which value the lifetime increase saturated. These data, together with measured perovskite stoichiometry, indicate that equal numbers of Ca and Ti vacancies were the prime charge compensators. Thermal gravimetric data are consistent with charge compensation occurring via the cation vacancies in the air-fired samples and Ti3+ in equivalent samples prepared under reducing conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.00045.x
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  • 2
    Electronic Resource
    Electronic Resource
    Crystal Chemistry and Stabilization in Air of Brannerite, UTi2O6 (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Brannerite, UTi2O6, can be formed only under low oxygen pressures by dry ceramic processing techniques, but the substitution of ∼0.2 and 0.3 formula units (fu) of Ca or Gd, respectively, for U allows the stabilization of the phase in air. The Ca/Gd in brannerite provides charge compensation for some U to exist in valence states 〉+4, as found by X-ray absorption spectroscopy of the U LIII-edge. The maximum solubilities of Ca and trivalent rare earths in the air-fired samples, 0.3 and 0.5 fu, respectively, correspond to U having an average valence of +5. Ca and Gd had maximum solubilities of 0.2 and 0.45 fu, respectively, in argon-fired samples. An absorption band at 1448 nm in both air- and Ar-fired U-brannerite doped with Ca and Gd was observed using diffuse-reflectance spectroscopy and attributed to an electronic transition of U5+. A similar band was observed in an annealed natural brannerite, which contained Ca, rare earths, and Th, although the band was present at ∼1520 nm in the unannealed, X-ray amorphous sample. In synthetic ThTi2O6 (thorutite, having the brannerite structure), the solubility of Ca was undetectable and that of rare earths 〈0.1 fu. Other ionic substitutions in synthetic brannerites involved Hf, Pu, La, and Y for U, (Gd + Nb) for U + Ti, and Fe in the Ti site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00621.x
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  • 3
    Electronic Resource
    Electronic Resource
    Chemical diffusion of (La,Sr)CoO3 and (La,Sr)FeO3 (2000)
    Springer
    Journal of materials science 11 (2000), S. 691-696 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The present work reports equilibration kinetics for (La0.8,Sr0.2)CoO3(LSC) and (La0.72,Sr0.18)FeO3(LSF) in the temperature range 876–1114 K using a gravimetric method. Chemical diffusion determined in this way that depends on oxygen partial pressure, can be expressed by the following temperature dependence at low and high O2), respectively, for LSC: $$D_{chem} = 8.7 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {58.1 \pm 8.5} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (1)}}$$ $$D_{chem} = 6.2 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {75.4 \pm 6.5} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (2)}}$$ and for LSF: $$D_{chem} = 3.05 \times 10^{ - 5} {\text{exp}}\frac{{{\text{ - }}\left( {30.3 \pm 2.8} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (3)}}$$ $$D_{chem} = 6.3 \times 10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {82.7 \pm 10.2} \right){\text{kJ/mol}}}}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (4)}}$$
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008926809900
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  • 4
    Electronic Resource
    Electronic Resource
    Equilibration kinetics of (La,Sr)MnO3 (2000)
    Springer
    Journal of materials science 11 (2000), S. 697-702 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The present work reports isothermal changes of oxygen non-stoichiometry for the perovskite-type electrode material (La0.8Sr0.2)MnO3 in the temperature range 945–1255 K. A thermogravimetric method was used to monitor the rate of the gas/solid equilibration. For equilibration degrees larger than 0.5, the equilibration kinetic data can be described by a diffusion equation. The determined chemical diffusion coefficient depends essentially on the oxygen partial pressure. Its temperature dependence can be expressed by the following expressions at low and high p(O2), respectively: $$D_{chem} = (1.9 \pm 1.6)10^{ - 3} {\text{exp}}\frac{{{\text{ - }}\left( {{\text{83}}{\text{.4}} \pm {\text{15}}{\text{.8}}} \right){\text{kJ mol}}^{{\text{ - 1}}} }}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (1)}}$$ $$D_{chem} = (1.6 \pm 0.6)10^{ - 1} {\text{exp}}\frac{{{\text{ - }}\left( {{\text{121}}{\text{.2}} \pm 8.2} \right){\text{kJ mol}}^{{\text{ - 1}}} }}{{RT}}({\text{cm}}^{\text{2}} {\text{s}}^{{\text{ - 1}}} ){\text{ (2)}}$$
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008978810809
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  • 5
    Electronic Resource
    Electronic Resource
    X-ray diffraction and leaching of CsAlSi5O12 and CsZr2(PO4)3 irradiated by argon (3 MeV) ions (1984)
    Springer
    Journal of materials science 19 (1984), S. 2943-2947 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Metamict damage cross-sections for the candidate nuclear fuel waste immobilization materials CsAlSi5O12 and CsZr2(PO4)3 irradiated with 3 MeV argon ions were found to be 0.6±0.2 nm2 and 0.7±0.3 nm2, respectively, from powder X-ray diffraction measurements. Based on caesium extraction into solution, heavy irradiation produced increases of up to a factor of 25 in the dissolution rates of the materials in deionized water and a brine at 100° C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01026971
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  • 6
    Electronic Resource
    Electronic Resource
    Studies of the reaction between diamond and heated kimberlite (1974)
    Springer
    Contributions to mineralogy and petrology 47 (1974), S. 237-244 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract At temperatures above about 1100° C degassed molten kimberlites were found to attack diamond, producing both graphite and metallic iron on the diamond surface. Using ordinary kimberlites in experiments performed at 1 Kb in a closed system, diamonds developed etch features (at temperatures above about 1000° C), consistent with attack by wet CO2, but no graphite or iron was formed on the surfaces of the diamonds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390148
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  • 7
    Electronic Resource
    Electronic Resource
    Induced graphitisation around crystalline inclusions in diamond (1972)
    Springer
    Contributions to mineralogy and petrology 35 (1972), S. 227-234 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In an external vacuum and at temperatures between 900° C and 1650° C internal graphitisation takes place on or around mineral inclusions in diamond, and appears to be responsible for similar features previously reported in diamond from several localities. Several mechanisms are proposed and discussed for internal graphitisation at temperatures as low as 900° C: it is proposed that at low external pressures CO2 exsolves from inclusions and causes internal graphitisation. The results also indicate that immediately after pressure release arising from volcanic breakthrough of kimberlites of different geological ages at several localities in West and South Africa, the temperature was not in excess of 800° C to 900° C in certain regions of the diatremes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371217
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  • 8
    Electronic Resource
    Electronic Resource
    Radiation damage in natural titanites (1985)
    Springer
    Physics and chemistry of minerals 12 (1985), S. 255-260 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Natural titanites which have incurred radiation damage from the decay, over geologic time, of U and Th incorporated in the samples have been studied by powder X-ray diffraction, differential thermal analysis and infrared spectroscopy. In agreement with previous studies of ionirradiated synthetic titanite, X-ray diffraction indicated that titanite is two to three times more sensitive than zircon to damage from α-decay processes. Differential thermal analysis of samples which were deduced to have accumulated 10–30 percent of the α-fluence required to render the structure completely X-ray amorphous gave a series of exothermic peaks in the 200–800° C range of temperature. In such samples, X-ray and density measurement showed that atomic displacement damage anneals during heating periods of the order of one h in the temperature range 500–800° C. The density of titanite rendered X-ray amorphous by irradiation was estimated to be ∼8 percent lower than that of crystalline titanite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310337
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  • 9
    Electronic Resource
    Electronic Resource
    Electron paramagnetic resonance, optical absorption, and magnetic circular dichroism studies of the CO 3 − molecular-ion in irradiated natural beryl (1977)
    Springer
    Physics and chemistry of minerals 1 (1977), S. 165-178 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Room temperature X-irradiation of some natural beryls produced several new absorption lines in the electron paramagnetic resonance (EPR) spectrum, a known series of optical absorption lines in the 500–700 nm range, and a shift of the absorption edge to lower energies. Several of the new EPR lines and part of the irradiation-induced shift of the absorption edge disappeared after a few days at room temperature, and were not examined in detail. However, three of the paramagnetic centres responsible for the new EPR lines were stable at room temperature and two of these have previously been identified as atomic hydrogen and the methyl radical, CH3. These species were stable to ∼150 and ∼450°C respectively. The third stable species, hitherto unreported, showed a single-line EPR spectrum of axial symmetry, with g∥=2.0051 and g⊥=2.0152. This spectrum was found to be intensity-correlated with the series of optical bands in the 500–700 nm range, after thermal bleaching at 175°C. The EPR and optical spectra are therefore assigned to the same species. It is argued that this species is the CO 3 − molecular ion, located in the widest part of the structural channel and aligned with the plane of the molecule perpendicular to the c axis. The EPR spectrum is consistent with a 2 A′2 ground state of a CO 3 − molecule with trigonal symmetry, and this requires that the optical transition has a 2 A′2 → 2 E′ character. Most of the features in the optical spectrum can be assigned to coupling of a totally symmetric mode of frequency ∼1020 cm−1 onto a zero-phonon line at 14,490 cm−1 and a second weaker line at 16,020 cm−1. However, both of these two fundamental lines are structured, and the two components show strong temperature-dependent derivative-shaped magnetic circular dichroism (MCD). Furthermore, the overall sign of the MCD for the line at 16,020 cm−1 is opposite to that at 14,490 cm−1. The separation (∼120 cm−1) of the two components of the 14,490 cm−1 line is much larger than that expected from spin-orbit interaction, and the origin of this splitting is not yet understood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307316
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  • 10
    Electronic Resource
    Electronic Resource
    Positron annihilation lifetime spectral changes on dehydration of natural beryls and cordierites (1980)
    Springer
    Physics and chemistry of minerals 6 (1980), S. 47-53 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The effect on positron annihilation lifetime spectra, measured at room temperature, of the dehydration of single crystals of beryl and cordierite was studied. In each case, the spectra were satisfactorily fitted to three lifetime components. For the beryls, the dehydration considerably enhanced the intensity of the intermediate-lifetime component (I 2) and reduced the intensity of the longest-lived component (I 3). I 2 is attributed to positron annihilation in the empty cages in the channels of the beryl structure and I 3 to annihilation by a pick-off process via unknown foreign molecules. However, for the cordierites, the main effect of the dehydration was a slight (∼10%) increase in the lifetime of the intermediate component, τ2. Here I 2 was relatively high both before and after dehydration and the increase in τ2 is attributed to Si-Al ordering. No changes in the lifetime spectra were produced by γ irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00308393
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