Lecture: Solid State Chemistry
(Festkörperchemie)
Part 2
(Further spectroscopical methods, 15.7.04)
H.J. Deiseroth, SS 2004
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Orders of magnitude in size  microscopic techniques
2
Orders of magnitude in energy
 spectroscopic techniques
3
Orders of magnitude in electrical conductivity
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Impedance spectroscopy (basic aspects)
Purpose: Exploring the electrical behavior of a microcrystalline
solid sample as function of an alternating current (ac) with a
variable frequency.
(note: difference between ac-/dc- and ionic/electronic conduction !!!)
three basically different
regions for the exchange
interactions between
current and sample:
a) inside the grains
(„bulk“)
b) at grain boundaries
c) surface of the
electrodes
the electrical behavior is simulated by a suitable combination of RC
circuits: R = resistivity, C = capacity
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Impedance spectroscopy (electrical quantities)
The direct current (dc) resistance (R) is defined as:
U
R
I
U: applied voltage (V), I: curent (A)
R: resistance ()
The alternative quantity for an alternating current (ac) is the
impedance (Z*) which, however, is a more complex quantity than R
because there is a phase shift between U and I in general.
ac-voltage: U(t) = U0sint
I(t) = I0 sin(t+)
(t: time,  = 2 with : frequency)
(: phase angle)
further details in
a separate talk
by Holger Mikus
this afternoon
If only capacities are present the phase shift between voltage and
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current amounts to /2 = 900.
ESCA: Photoemission or Photoelectron spectroscopy
ESCA = Electron Spectroscopy for Chemical Analysis
Basic equation: Eout = h - Ebind.
UV or
X-Ray
h
Int.
e- (Eout)
UHV
solid
Ebind.
strong
h
Eout
weak
Ebind.
- the higher the binding energy
(Ebind.) the lower the Eout !
- ESCA is in particular a surface
sensitive method (UHV !)
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ESCA: Photoemission or Photoelectron Spectroscopy
Exciting Radiation
Outcoming Radiation
UV (~ 20 eV)  UPS
electrons from
occupied valence states
X-Ray (~ 10 keV)  XPS
electrons from
(occupied) core states
-commercial laboratory based spectrometers (UHV-technique) are available
but relatively expensive and of limited versatility !
- more promising for the future is the use of synchroton radiation:
 continuous spectrum of exciting radiation (UV  X-Ray)
- intensity of synchroton radiation is orders of magnitudes higher !
(e.g. angle resolved detection of outcoming radiation is possible
- detection of „orbital shapes“)
- polarization of synchroton radiation allows spin polarized experiments8
Synchroton Storage Ring
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Synchroton Radiation
Source of
radiation
Magnitude of
wavelength
Type of
radiation
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ESCA: Photoemission or Photoelectron spectroscopy
- analysis of the energy levels of electrons in molecules („chemical shift“)
- band structure of solids
S2O32-
KCr3O8
Eout
Ebind.
Eout
Ebind.
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ESCA: Photoemission or Photoelectron spectroscopy
ESCA = Electron Spectroscopy for Chemical Analysis
UV or
X-Ray
e-
UPS spectrum
UHV
DOS
(below EF, occupied
states only)
solid
The „energy spectrum“ of the
emitted electrons is analyzed !
- energy
- momentum
- spin
Band structure
(chemical bonding in
different directions
of a crystalline solid)
energy
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Moessbauer Spectroscopy
 the nucleus of the specific isotope of an atom embdedded
in a solid (e.g. 57Fe) is excited by -rays emitted by an instable
isotope of a neighbor element (e.g. 57Co)
„Chemical shift“
and „Hyperfine
splitting“
source:
57Co
e.g.
(tunable)
Doppler effect
absorber:
e.g.
57Fe
frequently applied for
 57Fe, 119Sn, 127J ...
 chemical surrounding (symmetry,
coordination number, oxidation
state, magnetism) of atoms with
these nuclei in a solid can be probed
in a highly sensitive way (~10-8 eV)
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Moessbauer Spectroscopy
Two major informations from
Moessbauer spectra:
a) „Chemical Shift“
(not to be confused with the same
term in NMR and ESCA)
 oxidation state
b) Hyperfine Splitting
 magnetic interactions
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EXAFS and XANES
Spectroscopical methods associated with specific physical
effects at/near characteristical X-ray absorption edges:
EXAFS: Extended X-Ray Absorption Fine Structure
XANES: X-Ray Absorption Near Edge Structure
- tunable synchroton radiation in the X-Ray region necessary
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Thermal Analysis
DTA: Differential Thermal Analysis
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TG: Thermogravimetry
(mass change during heating or cooling combined with DTA)
Hysteresis 
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Thermal Analysis
DSC: Differential Scanning Calorimetry
- Quantitative measurement of enthalpy changes
TMA: Thermo Mechanical Analysis („dilatometry“)
- Mechanical changes that occur upon temperature changes
(see lab courses in inorganic chemistry and construction materials
chemistry)
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