Inorganic and Nanomaterials Flashcards
Long Range Order
crystalline
continuum of order
Short Range Order
amorphous
continuum of order
ReO3
vertex sharing octahedral
TiO2
rutile
anatase
brockite
Carbon Allotropes
graphite
diamond
fullerene
Defects
0 K perfect crystallinity
thermodynamics drive defect formation
requires input of energy
increased entropy
Intrinsic Defects
Schottky - vacancies present
Frenkel- displacement of an ion moving between
n(s/f) = Nexp(-deltaH(s/f) / 2kT)
Extrinsic Defects
introducing ions
doping
electron donating atom e.g. K+
electron can be a suited into conduction band
Non-Stoichiometry
defects and doping
TiO same as NaCl Rock salt
TiOx 0.7 1 titanium vacancies
Solid Solution Non-Stoichiometry
substitutional - new atom replaces existing
interstitial - atom added
Long Range Ion Movement
Li Ion Batteries
C6 + LiMn2O4 —> LixC6 + Li1-xMn2O4
2 x electrodes 1 x electrolyte
layers, channels, pores provide holes for Li+
intercalation xLi + C6 –> LixC6
deintercalation LiCoO2 –> xLi+ + e- + LixCoO2
0
Ecell
Ecell = Eanode - Ecathode W = V x A Ah = A x h E = W x h
Localised Ion Movement
radio, radar, sonar, ultrasound
ion in asymmetric site
local dipole movement
Ferroelectrics
apply electric field to displace an ion
high dielectric strength: not break down at high voltage
low dielectric loss: not lose electrical energy as heat
stored charge can be measured in parallel plate
Q = CV
Er = Cdielectric/Cvacuum
BaTiO3 Perovskite
> 120C Ti in symmetrical Oh
thermal motion generates sufficient chemical pressure to stabilise cubic structure
5-120C Ti displaced resulting in polarisation
motion reduced, structure distorts
Piezoelectrics
polarise under action of mechanical stress - pressure
tetrahedral groups
alternating electri. field causes vibrations
Pyroelectrics
polarisation which is temperature dependent
thermal expansion/contraction of lattice
changes the size of the dipoles
Paramagnetism
unpaired electrons
magnetic dipoles do not interact
temperature decreases, dipoles align parallel with the field
Antiferromagnetism
no applied field needed to align dipoles
spins anti-parallel
Tn Neel: antiferromagnetic-paramagnetic transition
Ferromagnetism
cooperative magnetism where applied field not needed to align spins
spins parallel
Tc Curie: ferromagnetic-paramagnetic transition
Ferrimagnetism
cooperative magnetism where applied field not needed to align spins
spins anti-parallel with partial cancellation
Superexchange
interaction of metal ions mediated by anions
overlap atomic orbitals
Leading to Antiferromagnetism
metal monoxides
Rock salt structure
Oh sites
2 x eg each containing unpaired electrons
Leading to Ferrimagnetism
2 sublattices, 1 with greater magnetic moment than the other electrically insulating 2 metal sites spinel: [A2+]tet[B3+]oct inverse spinel: [B3+]tet[A2+,B3+]oct M3+ prefers octahedral small cation prefers tetrahedral
Domains
not all Fe magnetic at room temperature
apply a magnet next to it - magnetises
below Tc temperature
antiparallel–flux generated– magnetic
Demagnetised
cohesive field
Superconductivity
zero electrical resistance
Meissner: external. angelic field ejected
large magnetic field generated
support large currents without resistive heating
Cup rates
high Tc
CuO2 planar layers separated by charge
reservoir layers control Cu oxidation states
Borises
MgB2
B in interstites of Mg
hexagonal layers
Fullerides
intercalation of metals into C60 lattice
electron transfer to C60
electrons move through layers
Cooper Pair
mutual attraction of electrons
attraction of electron to lattice ion
lattice distorts slightly
second electron attracted by ion displacement electron-phonon coupling
Wet Chemical Method
prepare soluble nanoparticles
prevent aggregation causing precipitation
coat surface
bulky ligands, fatty acids, amines, thiols
size and shape can be controlled
X-Ray Diffraction
single crystal m des
width of peak increases with size
t = ky/ Bcos@
Semiconductor
conduction band
photon absorbed
exciton generated
relaxation leads to luminescence
