Recent advances in intercalation compounds physics

1
Recent advances in intercalation compounds physics
2

• Intercalation of TiSe2 with Ag and transition
  metals leads to formation of polarons which are
  the deformation centers of lattice and traps for
  electrons. Corresponding band of impurity states
  with binding energy 0.3 eV was observed
  with ARPES. Behavior of these polarons is
  determined by competition of two effects
• energy gain as a result of decrease of EF because
  of the appearing of impurity polaron band
• energy loss because of deformation of lattice
• Constants of elastic forces are temperature
  dependent, which leads to
  non-monotone dependence of localization degree
  of charge carriers.
• State of localization centers and lattice
  deformation affect on interaction between centers
  and their ordering.

3
Mn0.145TiSe2

• Single crystals of Mn intercalated in TiSe2 have
  been obtained for a first time.
• Measurements of resistivity carried out on 2 x 2
  mm2 large crystals using a standard 4-contact
  methodic.
• One can see a difference between a resistivity
  along layers and a resistivity in normal to
  layers direction.
• Presence of charge-density-wave transition at
  100 K.

4

• Red curve Mn0.145TiSe2, in basal plane
• Black curve TiSe2
• On the inset Mn0.145TiSe2, in normal to layers
  direction

5
AgxTiSe2

• Deposition of 2 monatomic layers of Ag (6 Å) on
  TiSe2 surface in chamber of spectrometer with
  consequent annealing ( 250 0C, 2 hours) let us to
  see the changes in XPS spectra and in LEED before
  and after annealing.
• LEED photographs show the appearance of
  superstructure after deposition of Ag
• Valence band spectra shows that Ag dissolves in
  TiSe2 (appearance of Se after annealing)

Spectroscopy experiments were carried out on
ESCALAB-5 spectrometer in Solid State Physics
Institute, Chernogilovka, Russia, in April and
July, 2006.
6
AgxTiSe2 LEED
TiSe2 0.5 ML (1.5 Å) Ag
TiSe2
TiSe2 2 ML (6 Å) Ag, before annealing
TiSe2 2 ML Ag, after annealing
7
XPS of TiSe2 with deposited Ag
Appearance of additional peaks after annealing
leads to conclusion that Ag dissolves in TiSe2
8
(No Transcript)
9

• The intercalation of TiSe2 with transition metals
  and Ag leads to formation of polarons, which
  localization degree is temperature dependent. At
  specified temperature the highest localization
  degree (polaron band collapse, PBC) is observed.
  This phenomena is conducted by the high
  distortion of the lattice and the low mobility of
  polarons. This effect was earlier observed in
  compounds AgxTiTe2 on the unit cell volume
  versus temperature curve there is a local minimum
  at TPBC 150 0C. Moreover, at this temperature
  the drastic change of conductivity is observed.

Unit cell volume versus temperature for AgxTiTe2
near PBC at Ag concentrations x 0.65 ( curve 1)
? 0.75 (curve 2)
Conductivity versus temperature for AgxTiTe2 with
various concentration of Ag near PBC (150?C ore
423 K).
10
FexTiSe2
DTA data revealed two anomalies
Electroconductivity versus quenching temperature
for FexTiSe2. One can see that samples quenched
from high temperatures have high
electroconductivity.
DTA for Fe0.25TiSe2 (sample was quenched after
annealing at 300?C for 1 week)
11
FexTiSe2
Elastic neutron scattering experiment was carried
out on High Resolution Fourier Difractometer in
Joint Institute for Nuclear Research, Dubna,
Russia in April, 2006.
Diffraction reflexes width versus temperature for
Fe0.25TiSe2
Lattice parameter c and unit cell volume versus
temperature for Fe0.25TiSe2
12
FexTiSe2

• It were researched interactions between centers
  Ti Fe - Ti, leading to ordering of intercalant
  and FexTiSe2 (x 0?0.5) samples, obtained with
  different thermal conditions.
• Slowly cooled samples, enriched with iron,
  revealed ordering with space group I12/m1

Bond length iron - titan?? slowly cooled
samples ???. quenched samples
13
Modification of phonon spectra of TiSe2 by
intercalation

• Phonon DOS of M0.25TiSe2.