Sergey L. Bud’koHyperfine Parameters Chemical Isomer Shift (IS) (δδδδ): Arises out of the...
Transcript of Sergey L. Bud’koHyperfine Parameters Chemical Isomer Shift (IS) (δδδδ): Arises out of the...
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Mössbauer Spectroscopy
590B S09
Sergey L. Bud’ko
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Sergey L. Bud’ko(Сергей Леокадьевич Будько)
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Nobel Prize in 1961 for PhD work of 1958
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Mössbauer spectroscopy and its sensitivity
Mössbauer spectroscopy is a technique in which interactionbetween the electromagnetic moment of the nuclear charge andelectromagnetic field produced by the extra-nuclear electrons arestudied. This interaction gives splitting/shifting of the nuclearenergy levels.
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For the most common Mössbauer isotope, 57Fe, the linewidth is
5x10-9eV. Compared to the Mössbauer gamma-ray energy of
14.4keV this gives a resolution of 1 in 1012 (or the equivalent of a
small speck of dust on the back of an elephant or one sheet of
paper in the distance between the Sun and the Earth).
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Emission Absorption
Free emitting and absorbing atoms
Recoil
mc
E=E
2
2
R
2
γEnergy of recoil
γ-ray energy
Mass of atomafter Enver Murad, Workshop on Martian Phyllosilicates, 2008
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Emission Absorption
Emitting and absorbing atoms fixed in a lattice
No recoil
Mc
E=E 2
2
R
2
γ
Mass of particle
Mössbauer spectroscopy is the recoil-free emission and absorption of γ-rays
(VERY LARGE)
after Enver Murad, Workshop on Martian Phyllosilicates, 2008
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Experimentally:
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Experimental
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Experimental
Mostly in transmission mode
Source (emitted radiation: resonant γ-rays (recoil-free), non-resonant γ-rays (involving recoil), radiation from all other transitions, secondary radiation (mainly X-rays) produced in the matrix)
57Co in Rh matrix: activity: 5 mCi to 150 mCi
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57Co in Rh matrix: activity: 5 mCi to 150 mCi
119mSn in Ca-stannate matrix: 2-25 mCi
Absorber – your sample (“usually” powder, can use single crystals, thickness is an issue)
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Experimental
Drive system (mechanical, electromechanical, piezoelectric, hydraulic, etc.) Constant-velocity and sweep-velocity systems. Usually the source makes the motion.
Up to 300 mm/s (1000 mm/c);
Resonance frequency ~ 25 Hz
Different modes allowed
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Different modes allowed
~25 mm/s per Volt
---------------------------------------------------
(and if you are really cheap you can try to use old speaker)
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Experimental
Detector (scintillation detectors, proportional counters, lithium-drifted germanium or silicon detectors).
Proportional counter – Ar/Kr/Xe filled, ~ 2 kV operating voltage.
Also need a lot of electronics, cryostat/furnace, ME fitting software
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cryostat/furnace, ME fitting software
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Hyperfine Parameters
Chemical Isomer Shift (IS) (δδδδ): Arises out of the interactionbetween nuclear charge density and the surrounding ‘s’ electroncharge cloud. IS can give information about the spin state as wellas the co-ordination number.
Quadrupole Splitting (QS) (∆∆∆∆): Arises due to interaction between the
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Quadrupole Splitting (QS) (∆∆∆∆): Arises due to interaction between the
electric quadrupole moment of the nucleus and Electric Field
Gradient created by the electrons. QS can give information about
the charge symmetry around the nucleus.
Hyperfine field (Hint) It gives the internal magnetic field of a
magnetic material
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Isomer Shift
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Quadrupolar Splitting
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Magnetic Hyperfine Field
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Magnetic Dipole + Electron Quadrupole Interactions
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can get some idea about the magnetic moment direction
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“IDEAL” Mössbauer spectra - summary
Depending on the local environments of the Fe atoms and the magnetic properties, Mössbauer spectra of iron oxides can consist of a singlet, a doublet, or a sextet.
Phyllosilicates, 2008
Symmetric charge
No magnetic field
Asymmetric charge
No magnetic fieldSymmetric or asymmetric charge
Magnetic field (internal or external)
∆ Bhfδ Isom
er
shift
Quadru
pole
split
ting
Magnetic h
yperf
ine f
ield
after EnverMurad, Workshop on Martian Phyllosilicates
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e T
ran
sm
issio
n
∆
Fe3+
-4 -2 0 2 4
Velocity (mm/s)
Rela
tive
δFe2+
-4 -2 0 2 4
Velocity (mm/s)
after Enver Murad, Workshop on Martian Phyllosilicates, 2008
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Use of Mössbauer spectroscopy as a “fingerprinting” technique
3
4
[6]Fe2+
[8]Fe2+
[5]Fe3+
Isomer shifts and quadrupole splittings of Fe-bearing phases vary systematically as a function of Fe
1.0 1.5
1
-0.5 0.5
Isomer shift (mm/s)
0
2
0.0
[6]Fe(II)
[6]Fe(III)[6]Fe3+
[4]Fe3+
[4]Fe2+
[sq]Fe2+
[5]Fe3+
[5]Fe2+
as a function of Fe oxidation, Fe spin states, and Fe coordination.
Knowledge of the Mössbauer parameters can therefore be used to “fingerprint” an unknown phase.
after Enver Murad, Workshop on Martian Phyllosilicates, 2008
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ME applications: Fe – containing minerals on Mars
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Mars
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Mars surface geology
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Examples
Pressure-induced magnetic order
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J.P.Sanchez et al., Hyperfine Interactions…
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Examples
TbNi2B2C (actually, Tb(Ni0.9957Fe0.01)2B2C)
TWFM
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TN
D. Sanchez et al, PRB
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Examples
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RNi2B2C
Fe replaces Ni, both are non-magnetic in these materials
No HF field on 57Fe
Possibly collinear AFM (consistent with earlier neutron data)
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Examples
CeFeAs(O/F)
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neutron scattering
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Examples
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D.Sanchez et al. + Ames Laboratory
unpublished
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Mössbauer Spectroscopy
“cheap”
“fast”
sensitive to magnetic transitions, phase purity
can give some information about the nature of the magnetic phase
local probe
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local probe
reasonably easy to use T, P, H as variables
limited number of isotopes
interpretation somewhat model/fit dependent
NEED TO USE IN CONJUNCTION WITH OTHER MEASUREMENTS
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timescales associated with some spectroscopic techniques
Energy of excited state Typical relaxation Typical
Technique (Hz) time (seconds) linewidth (Hz)
NMR (solution) 108 10 10-1
ESR (solution) 1010 10-5 105
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rotationalspectroscopy (gas) 1011 10-4 104
vibrationalspectroscopy (gas) 1014 10-8 108
electronicspectroscopy (solution) 1016 10-15 1015
Mössbauerspectroscopy (solid) 1019 10-8 108
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Reading materials
Mössbauer Spectroscopy and its Applications, T E Cranshaw, B W Dale, G O Longworth and C E Johnson, (Cambridge Univ. Press: Cambridge) 1985
Mössbauer Spectroscopy, D P E Dickson and F J Berry, (Cambridge Univ. Press: Cambridge) 1986
The Mössbauer Effect, H Frauenfelder, (Benjamin: New York) 1962Principles of Mössbauer Spectroscopy, T C Gibb, (Chapman and Hall: London) 1977
Mössbauer Spectroscopy, N N Greenwood and T C Gibb, (Chapman and Hall:
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Mössbauer Spectroscopy, N N Greenwood and T C Gibb, (Chapman and Hall: London) 1971
Chemical Applications of Mössbauer Spectroscopy, V I Goldanskii and R H Herber ed., (Academic Press Inc: London) 1968
Mössbauer Spectroscopy Applied to Inorganic Chemistry Vols. 1-3, G J Long, ed., (Plenum: New York) 1984-1989
Mössbauer Spectroscopy Applied to Magnetism and Materials Science Vol. 1, G J Long and F Grandjean, eds., (Plenum: New York) 1993