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  • 1
    Electronic Resource
    Electronic Resource
    Protons and other defects in Fe-doped KTaO3 (1992)
    Springer
    Applied physics 55 (1992), S. 324-331 
    Details
    ISSN: 1432-0630
    Keywords: 61.70−r ; 66.10.Ed ; 76.30.Fc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The properties of defects in Fe-doped KTaO3, both in the form of single crystals and polycrystalline ceramics, have been investigated for a wide range of Fe concentrations. The techniques employed included infrared (IR) absorption, electron paramagnetic resonance (EPR), and ac electrical conductivity together with complex-impedance analysis. Samples were pretreated (at 900° C) in water vapor to introduce protons which take the form of OH· O defects, and were also treated at various oxygen partial pressures. A calibration of the OH− IR absorption band was carried out with the aid of a deuterium nuclear-probe method. EPR showed cubic and axial Fe3+ spectra, but only the axial spectrum appeared for crystals with high Fe concentrations. Pre-dominantly proton conductivity was observed for samples treated in reducing atmospheres, and a proton-hopping activation energy of 0.73 eV was deduced. For samples treated in high oxygen pressures, however, hole conduction dominated. Evidence for proton interaction effects was also found, but the nature of the traps is not clear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324079
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  • 2
    Electronic Resource
    Electronic Resource
    Static and dynamical properties of D0i (Li) in MgO:Li studied by EPR: Isotope effects (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2976-2980 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The D0i (Li) defect has been formed in MgO:Li and studied by EPR. The static spin Hamiltonian parameters, obtained from the angular dependence of the spectrum at LNT, are given and compared with those of H0i (Li). A noticeable isotope effect is found in the lithium shf interaction, which is explained as a consequence of the zero-point vibration of the hydrogen atom. The temperature evolution of the spectrum was also studied, and interpreted as a motional averaging process due to the reorientation of the defect among its eight equivalent 〈111〉 sites. Using the Liouville stochastic formalism, the EPR spectra were simulated as a function of the jump frequency (ωe) and fitted to the experimental ones. This yields the temperature dependence of ωe which can be compared with that for the H0i (Li) defect. The isotope effects found, both in the activation energy and in the preexponential factor, are interpreted in the frame of the small-polaron theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453991
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  • 3
    Electronic Resource
    Electronic Resource
    Electron paramagnetic resonance investigations of divalent cobalt in single crystals of perovskite (CaTiO3) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5117-5118 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron paramagnetic resonance (EPR) spectrum of Co2+ in CaTiO3 was observed at 9 GHz in the temperature range of 10–15 K. The results establish that Co2+ occupies four magnetically inequivalent sites in the orthorhombic CaTiO3 lattice. These sites become equivalent when the applied magnetic field is parallel to the so-called "pseudocubic'' b axis of the crystal. The magnetic axes in the plane perpendicular to the pseudocubic axis make an angle of ±28.5°±0.5° with the a and c axes of the host lattice. The site symmetry is qualitatively similar to that of the aliovalent ions Er3+ and Yb3+ in CaTiO3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457604
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  • 4
    Electronic Resource
    Electronic Resource
    EPR characterization of Er3+ and Yb3+ in single crystals of synthetic perovskite (CaTiO3) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5267-5272 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Synthetic perovskite (calcium titanate, CaTiO3) crystallizes in the orthorhombic structure with space group Pcmn (Z=4) and with lattice constants a=5.367, b=7.622, and c=5.425 A(ring). Single crystals of CaTiO3 doped with either Er3+ (4f11 electronic configuration) or Yb3+ (4f13 electronic configuration) were grown by means of a flux technique. A mixed KF–LiF flux and Pt crucibles were employed, and the CaTiO3 crystals were formed by spontaneous nucleation on slow cooling (1.0 °C/h) between 1250 and 875 °C. EPR spectra were observed for both Er3+ and Yb3+ at a frequency of ∼9 GHz and a temperature of ∼15 K. The EPR results establish that both Er3+ and Yb3+ occupy four magnetically inequivalent sites in the CaTiO3 lattice and that these sites become equivalent when the applied magnetic field is oriented parallel to the "pseudocubic'' b axis of the host synthetic perovskite crystal. The magnetic axes lying in the plane perpendicular to the b axis were found to make an angle with the a and c faces of the crystal that is equal to 21.0(5)° for Yb3+ and 11.5(5)° for Er3+. Isotopically enriched dopants were employed as an aid in analyzing the spectra, and the spin-Hamiltonian parameters have been determined for both rare-earth impurity ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452772
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  • 5
    Electronic Resource
    Electronic Resource
    EPR and thermoluminescence investigations of Mn2+ in LuPO4, YPO4, and ScPO4 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6113-6120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Divalent manganese has been incorporated in both single crystals and powders of the zircon-structure hosts LuPO4, YPO4, and ScPO4. The single-crystal specimens were grown by slowly cooling a Pb2P2O7 flux from 1360 °C, and finely divided powders of these materials were also prepared using a molten urea precipitation technique. Electron paramagnetic resonance studies have shown that tetragonal symmetry Mn2+ sites are present in both single crystals and powders of ScPO4 and LuPO4 but are not present in either YPO4 single crystals or powders. An orthorhombic symmetry spectrum was observed for Mn2+ in single crystals of all three hosts and in YPO4 powders. Orthorhombic spectra were not found in Mn2+ doped powders of ScPO4 and LuPO4. In the case of the orthorhombic-symmetry spectra, four sites were present in these tetragonal zircon-structure hosts. The sites were magnetically inequivalent but were equivalent in terms of the strength and symmetry of the crystalline electric field. The orientations of the orthorhombic-site principal axes relative to the crystallographic axes were determined in each case. The axial spin-Hamiltonian parameter b02 was found to be positive in the case of the tetragonal-symmetry sites and negative for the orthorhombic-symmetry spectra. Thermoluminescent properties of these materials were also investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449603
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  • 6
    Electronic Resource
    Electronic Resource
    The observation by EPR of trivalent hafnium in LuPO4, YPO4, and ScPO4 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2754-2758 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recent EPR studies of the 4d1 configuration ion Zr3+ in the tetragonal-symmetry orthophosphate hosts LuPO4, YPO4, and ScPO4, have led to additional investigations of d1 configuration ions associated with unusual valence states of other elements. Single crystals of LuPO4, YPO4, and ScPO4 doped with hafnium were grown and the electron paramagnetic resonance (EPR) spectrum of the 5d1 ion Hf 3+ was observed in all three cases. EPR signals due to trivalent hafnium were only observed, however, when the doped samples were gamma irradiated at 77 K and maintained at 77 K during the EPR observations. Since there are two odd isotopes of hafnium with different nuclear spins and different natural abundances, identification of the spectrum of Hf 3+ was straightforward. Since Hf 3+ represents such an unusual valence for hafnium in the solid state, however, this identification was unequivocally verified by preparing crystals doped with isotopically enriched 179Hf. The spectroscopic splitting factors, g(parallel) and g⊥, and the parallel magnetic hyperfine constants A(parallel) of 177Hf and 179Hf were obtained for Hf 3+ in all three hosts. A determination of the hyperfine parameters with the applied magnetic field oriented in the perpendicular direction was not carried out due to quadrupole effects. As in the case of Zr3+, the observed electronic g values for Hf 3+ could not be accounted for by the standard second-order equations which included the spin-orbit-induced admixture of some other excited orbital levels of the d1 configuration into the ground orbital level. The ratio of the nuclear magnetic moments 177μ/179μ, was determined to be 1.2361(4) and 1.2362(3) for hafnium in ScPO4 and LuPO4, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449225
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  • 7
    Electronic Resource
    Electronic Resource
    EPR observations of trivalent titanium in orthophosphate single crystals (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1-6 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state spectroscopic properties of the 3d1 electronic configuration ion Ti3+ have been investigated using EPR spectroscopy. Trivalent titanium was incorporated as a dilute impurity in single crystals of the tetragonal, zircon-structure hosts ScPO4, YPO4, and LuPO4. The EPR spectrum of Ti3+ was observed in the as-grown orthophosphate crystals, and low temperature irradiations were not required to produce the trivalent state. The EPR results show that Ti3+ occupies a substitutional cation site in the host orthophosphate single crystals. Axial spin-Hamiltonian parameters were determined at 77 K, and these results are compared to those obtained previously for the 4d1 and 5d1 configuration ions Zr3+ and Hf 3+ in the same host crystals. Titanium-doped orthophosphate crystals containing isotopically enriched 47Ti or 49Ti were also grown and employed in determinations of the hyperfine parameters. The g-values observed here for Ti3+, and determined previously for Zr3+ and Hf 3+ are not accounted for by the published second-order expressions indicating that additional coupling mechanisms are operative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451638
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  • 8
    Electronic Resource
    Electronic Resource
    Excited state absorption and fluorescence line narrowing studies of Cm3+ in LuPO4 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2539-2546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser selective excitation, fluorescence line narrowing, and excited state absorption techniques have been used to investigate the electronic-energy-level structure of the 5f7 ion Cm3+ in the host crystal LuPO4. Crystal-field levels have been determined up to 35 700 cm−1 for the principal D2d symmetry site. Eighty levels have been assigned and fitted to a parametric Hamiltonian with an rms deviation of 28.4 cm−1. Inhomogeneous broadening of the electronic transitions and the small 9.5 cm−1 splitting of the nominally 8S7/2 ground multiplet are responsible for satellite lines reported previously. Time resolved fluorescence line narrowing was used to observe energy transfer between different subsites of the intrinsic Cm3+ center. It was found that electric-dipole interactions mediate this energy transfer. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472118
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  • 9
    Electronic Resource
    Electronic Resource
    Neutron study of crystal-field transitions in ErPO4 : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6069-6071 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystal-field splitting of the Er3+ ground multiplet 4I15/2 in ErPO4 is investigated by inelastic neutron scattering. Four excitations from the Γ7 ground state to the excited states and several transitions between the excited states have been identified. The observed transition energies and intensities are used to refine the parameters of the crystal-field potential. The calculated magnetic susceptibility χ(T) agrees well with experimental values from single-crystal measurements. A comparison of the neutron data with optical absorption and both nonresonance and resonance Raman scattering measurements has been made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353472
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  • 10
    Electronic Resource
    Electronic Resource
    Spectroscopic studies of magnetic transitions in TbPO4 : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7030-7032 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In TbPO4, an antiferromagnetic-phase transition is accompanied by a cooperative Jahn–Teller effect involving a Tb ion-lattice coupling that induces a tetragonal-to-monoclinic distortion of the crystal lattice and an associated readjustment of the Tb electronic states as required by the lowering of the rare-earth-site symmetry. The laser-excitation and emission spectra of TbPO4 and 0.1% Tb-doped YPO4 single crystals were studied at temperatures below and above the phase transitions. The line shapes of transitions in the stoichiometric compound are unusually broad and asymmetric while those observed for the dilute compound are relatively sharp. In addition, the TbPO4 spectra show an anomalous temperature dependence near the phase transition, indicating strong interactions of the rare-earth ions with their local environments. In the present work, a comparison of the optical results with the results of new neutron-scattering measurements is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356769
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