30 May, 2009 30 May, 2009 ERICE 2009 ERICE 2009 1 Structural Structural r r espon espon s s e to e to p p ressure ressure i i nduced nduced e e lectronic lectronic t t ransitions ransitions in TM- in TM- compounds compounds Moshe Paz-Pasternak, Tel Aviv Moshe Paz-Pasternak, Tel Aviv University, ISRAEL University, ISRAEL Beware of false knowledge; it Beware of false knowledge; it is more dangerous than is more dangerous than ignorance ignorance George Bernard Shaw George Bernard Shaw
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Structural r espon s e to p ressure i nduced e lectronic t ransitions in TM-compounds
Structural r espon s e to p ressure i nduced e lectronic t ransitions in TM-compounds. Moshe Paz-Pasternak, Tel Aviv University, ISRAEL. Beware of false knowledge; it is more dangerous than ignorance George Bernard Shaw. - PowerPoint PPT Presentation
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30 May, 200930 May, 2009 ERICE 2009ERICE 2009 11
StructuralStructural r responesponsse to e to ppressure ressure iinduced nduced
eelectroniclectronic ttransitionsransitions in in TM-compoundsTM-compounds
Moshe Paz-Pasternak, Tel Aviv University, Moshe Paz-Pasternak, Tel Aviv University, ISRAELISRAEL
Beware of false knowledge; it is Beware of false knowledge; it is more dangerous than ignorancemore dangerous than ignorance
George Bernard ShawGeorge Bernard Shaw
30 May, 200930 May, 2009 ERICE 2009ERICE 2009
What types of electronic transitions What types of electronic transitions may lead to structural phase may lead to structural phase transition in TMC’s?transition in TMC’s?
o highhigh to to lowlow spin transitions spin transitionso Intra-band overlapIntra-band overlap; ; the the Mott-HubbardMott-Hubbard
– Appropriate electronic spectroscopy methods with Appropriate electronic spectroscopy methods with radiation that can be transmitted through radiation that can be transmitted through diamonds such asdiamonds such as::
– K-K-edge X-rays of the TM-ion to be used for XAS, XANES, edge X-rays of the TM-ion to be used for XAS, XANES, XES, EXAFS, etc.XES, EXAFS, etc.
– Mössbauer spectroscopy in iron-containing samplesMössbauer spectroscopy in iron-containing samples..– Optical spectroscopyOptical spectroscopy
- and- and– Wires for resistance and other electrical measurementsWires for resistance and other electrical measurements
30 May, 200930 May, 2009 ERICE 2009ERICE 2009
TheThe d d-shell -shell ((Hund’s rules)Hund’s rules)
The high spin state is unstable at high-The high spin state is unstable at high-pressurepressure
P“Spin
crossover”
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Fe3+(LS)) 5 ↑↓ ↑↓ ↓Fe3+(HS)) 5 ↑ ↑ ↑ ↑ ↑
Radius of TMRadius of TMHS HS > Radius of TM> Radius of TMLS
0 10 20 30 40 50 60 70 80 90
0.80
0.88
0.96
1.04
Pressure (GPa)
V/V
0
EuFeOEuFeO33
Fe3+(LS)Fe3+(HS)
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Mott Hubbard insulator Mott Hubbard insulator
The strong on-site Coulomb repulsion produces an energy gap, within the 3d band, known as the Mott-Hubbard gap (U).
The insulating gap may also arise from a finite ligand-to-metal p-d charge-transfer energy Δ. In the case of Δ <U we have a Charge-Transfer insulator.
1 1MHn n n nd d d d
1CTn nd d L (L - ligand hole)
- electronic configuration of the TM ion nd
U >
> U
B
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electronic/magnetic electronic/magnetic consequences consequences of Mott-Hubbardof Mott-Hubbard correlation- correlation-breakdownbreakdown
correlated statescorrelated states Uncorr. Uncorr. statesstates
insulatorinsulator metallicmetallic
OddOdd numbenumbe
r of r of spinsspins
HSHS LSLS
S S ≠ 0≠ 0 S S ≠ 0≠ 0 paramagneticparamagnetic
EvenEven numbenumbe
r of r of spinsspins
S S ≠ 0≠ 0 S S = 0= 0paramagneparamagne
ticticdiamagnediamagne
tictic
0S
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Mössbauer Mössbauer spectroscopyspectroscopy
That’s why we can use absorbers with
diam. <0.1 mm
The nuclear scattering The nuclear scattering cross-section of cross-section of
5757Fe(14.4 keV) gamma-Fe(14.4 keV) gamma-rays is ~ 10rays is ~ 109 9 barns!barns!
currently the best experimental method at the atomic currently the best experimental method at the atomic scale for studying magnetism at very high pressures scale for studying magnetism at very high pressures
HS > LS starting at ~ 90 GPaHS > LS starting at ~ 90 GPa
No symmetry or appreciable volume No symmetry or appreciable volume change ever detected.change ever detected.LS
HS
NaCl structureNaCl structure
Experimental proof of Hund’s ruleExperimental proof of Hund’s rulePPmechanicalmechanical > P > PCoulombicCoulombic
30 May, 200930 May, 2009 ERICE 2009ERICE 2009
-10 -5 0 5 100.92
0.96
1.00
velocity (mm/s)
inte
nsi
ty
Mg0.9
Fe0.1
O
5 K
78 GPa LSdiamagnetic
0 GPa HS antiferromagnetic
MgMg0.90.9FeFe0.10.1OO
0 10 20 30 40 50 60 70 80
0.4
0.6
0.8
1.0
0.0
0.5
1.0
Mg0.9
Fe0.1
O
low
-spi
n re
gim
e
high-spin regime
coex
iste
nce
regi
me
IS (
mm
/s)
Pressure (GPa)
QS
(m
m/s
)
low-spin data
high-spin data
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0 10 20 30 40 50 60 70
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
LP phaseIP phaseHP phaseDecompression
c/a
Pressure (GPa)
0 10 20 30 40
0
50
100
IS (
mm
/s)
Hhf(T
)T
N(K
)A
bund
ance
Pressure (GPa)
LP phase IP phase HP phase (metallic)
0
20
40
Hhf = H
S
Hhf = H
S-H
OHP phase
LP phase
IP phase
0.4
0.6
0.8
1.0
(d)
(c)
(b)
(a)
0
100
200
300
0 10 20 30 40 50 60 7045
50
55
60
65
70
75
80
85
90
95
100
Insulating (MH) phase
LP phaseHP phaseDecompression
Vol
ume
(Å3)
Pressure (GPa)
metallic phase-8 -6 -4 -2 0 2 4 6 8
7 GPa
18 GPa
Inte
nsity
Velocity (mm/s)
20 GPa
23 GPa
10 K 40 GPa
26 GPa
30 GPa
FeIFeI22
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FeFe((OOHH))22
Parise et alParise et al
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T >> TN
Paramagnetic Fe2+
T << TN
anti-ferromagnetic
Fe2+
2 3Fe Fe
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0 10 20 30 400.0
0.2
0.4
0.6
0.8
P
P
Fe+
3 ab
un
d.
P(GPa)
H Lateral displacement (Parise et al)Fe3+ abundance
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32
22( ) ( )PFe OH eFe OH
5 10 15 20
#
G L +
+
***
11
2
20
12
0011
111
0
10
210
1
10
0
00
1
28
18
11
5
1.5
P(GPa)
Inte
nsi
ty
2 (deg)
No change in structure!
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Conclusion
the orientation-disorder of the O-H dipoles the orientation-disorder of the O-H dipoles caused by the pressure-induced OH----HO caused by the pressure-induced OH----HO coulomb repulsion, and, coulomb repulsion, and,
to the exceptional small electron binding to the exceptional small electron binding energy of Feenergy of Fe2+2+
32
22( ) ( )PFe OH eFe OH
The irreversible oxidation process is attributed to:
Within the HP band-structure of Fe(OH)2 a new, localized band is formed populated by the “ousted” electrons
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Structural response to PI Structural response to PI electronic transitions in Feelectronic transitions in Fe3+ 3+
oxidesoxides
FeFe22OO33 ( (hematitehematite))
R R FeOFeO33 ((RR= rare-earth iron = rare-earth iron
perovskites)perovskites)
CuFeOCuFeO3 3 (delafossite)(delafossite)
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FeFe22OO33 a correlation breakdowna correlation breakdown
5 10 15 20
(a) 2.9 GPa
Inte
nsity
Diffraction Angle 2
*
(b) 46.0 GPa
Fig. 3
*
(c) 70.0 GPa
(d) Rh2O
3 II-type calc.
123
114
= 0.4246 Å
132
024
204
131
220
004
113
122
103/
211
200
11202
0
111
002
Rutile > RhRutile > Rh22OO33 II II
ΔΔVV/V/V00 = = 0.10.1
30 May, 200930 May, 2009 ERICE 2009ERICE 2009
FeFe22OO33 a catastrophic correlation a catastrophic correlation