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Title: Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe

Abstract

While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.

Authors:
 [1]; ;  [2];  [3];  [4];  [5]
  1. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
  2. Department of Physics and Astronomy, University of California, Irvine, California 92697-4575 (United States)
  3. Physics Department, University of California, Davis, California 95616 (United States)
  4. Materials Science Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
  5. Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634 (United States)
Publication Date:
OSTI Identifier:
20976629
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 1; Other Information: DOI: 10.1103/PhysRevB.75.012301; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BORON; CARBON; DEFECTS; GALLIUM COMPOUNDS; IMPURITIES; INELASTIC SCATTERING; NEUTRON DIFFRACTION; NEUTRON REACTIONS; STOICHIOMETRY; THERMAL EXPANSION; VALENCE; X-RAY SPECTRA; YTTERBIUM; YTTERBIUM COMPOUNDS

Citation Formats

Booth, C. H., Christianson, A. D., Lawrence, J. M., Pham, L. D., Lashley, J. C., and Drymiotis, F. R. Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.012301.
Booth, C. H., Christianson, A. D., Lawrence, J. M., Pham, L. D., Lashley, J. C., & Drymiotis, F. R. Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe. United States. doi:10.1103/PHYSREVB.75.012301.
Booth, C. H., Christianson, A. D., Lawrence, J. M., Pham, L. D., Lashley, J. C., and Drymiotis, F. R. Mon . "Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe". United States. doi:10.1103/PHYSREVB.75.012301.
@article{osti_20976629,
title = {Ytterbium divalency and lattice disorder in near-zero thermal expansion YbGaGe},
author = {Booth, C. H. and Christianson, A. D. and Lawrence, J. M. and Pham, L. D. and Lashley, J. C. and Drymiotis, F. R.},
abstractNote = {While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.},
doi = {10.1103/PHYSREVB.75.012301},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 1,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with nominally 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
  • While near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration, the NZTE mechanism remains elusive. We present x-ray absorption spectra that show unequivocally that Yb is nearly divalent in YbGaGe and the valence does not change with temperature or with 1% B or 5% C impurities, ruling out a valence-fluctuation mechanism. Moreover, substantial changes occur in the local structure around Yb with B and C inclusion. Together with inelastic neutron scattering measurements, these data indicate a strong tendency for the lattice to disorder, providing a possible explanation for NZTE in YbGaGe.
  • We investigate the effects of carbon and boron doping on the thermal expansion of the hexagonal (P6{sub 3}/mmc) intermetallic YbGaGe. X-ray powder diffraction was used to measure the lattice constants on pure and doped (C or B at nominal levels of 0.5%) samples from T{approx}10 K to T{approx}300 K. Also measured were resistivity, specific heat, and magnetic susceptibility. While the pure YbGaGe samples exhibit positive thermal volume expansion (V{sub 300K}-V{sub 10K})/V{sub 300K}=0.94, the volume expansion in the lightly C- or B-doped samples changes slope and tends toward zero-volume expansion. Such a strong response to light doping suggests that the underlyingmore » mechanism for the reported zero-volume expansion is substitutional disorder, and not the previously proposed valence fluctuations.« less
  • The structures of ordered and disordered {beta}-eucryptite have been determined from Rietveld analysis of powder synchrotron x-ray and neutron diffraction data over a temperature range of 20 to 873 K. On heating, both materials show an expansion within the (001) plane and a contraction along the {ital c} axis. However, the anisotropic character of the thermal behavior of ordered {beta}-eucryptite is much more pronounced than that of the disordered compound; the linear expansion coefficients of the ordered and disordered phases are {alpha}{sub a}=7.26{times}10{sup {minus}6}&hthinsp;K{sup {minus}1}; {alpha}{sub c}={minus}16.35{times}10{sup {minus}6}&hthinsp;K{sup {minus}1}, and {alpha}{sub a}=5.98{times}10{sup {minus}6}&hthinsp;K{sup {minus}1}; {alpha}{sub c}={minus}3.82{times}10{sup {minus}6}&hthinsp;K{sup {minus}1}, respectively. Themore » thermal behavior of {beta}-eucryptite can be attributed to three interdependent processes that all cause an increase in {ital a} but a decrease in {ital c} with increasing temperature: (i) Si/Al tetrahedral deformation, (ii) Li positional disordering, and (iii) tetrahedral tilting. Because disordered {beta}-eucryptite does not exhibit tetrahedral tilting, the absolute values of its axial thermal coefficients are smaller than those for the ordered sample. At low temperatures, both ordered and disordered {beta}-eucryptite exhibit a continuous expansion parallel to the {ital c} axis with decreasing temperature, whereas {ital a} remains approximately unchanged. Our difference Fourier synthesis reveals localization of Li ions below room temperature, and we suggest that repulsion between Li and Al/Si inhibits contraction along the {ital a} axes. {copyright} {ital 1999 Materials Research Society.}« less