The document summarizes the key electrical, magnetic, and dielectric properties of solids. It discusses how solids can be classified as conductors, insulators, or semiconductors based on their electrical conductivity. Semiconductors are further classified as intrinsic or extrinsic, with n-type and p-type extrinsic semiconductors discussed. Magnetic properties are also summarized, classifying materials as diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, or ferrimagnetic based on their behavior in magnetic fields. Finally, dielectric properties including piezoelectricity, pyroelectricity, ferroelectricity, and antiferroelectricity are briefly defined.

1. JFC Properties of Solids By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
Properties of Solids
The three main properties of solids which depend upon their structure are-
 1. Electrical properties
 2. Magnetic properties
 3. Dielectric properties
1. Electrical Properties of Solids
Electrical
Conductivity
Electronic Conductivity
(Metallic Conductivity)
Due to the motion of
electrons
(n-type Conduction)
Due to the motion of
positive holes
(p-type Conduction)
Ionic Conductivity
Due to the
motion of ions
 Electrical conductivity of metal is due to
motion of electrons and it increases with
the number of electrons available to
participate in the conduction process.
 Pure ionic solids are insulators. But the
presence of crystal defects increases their
conductivity.
 On the basis of electrical conductivity the
solids can be classified into three types
1. Conductors (metal)
2. Insulators
3. Semiconductors.
(V.B.)
(C.B.)
Conductors (Metal):
 Conductors are materials with
high conductivities, 𝝈 > 103
S/cm (like silver: 106
S/cm).
 They allow the maximum portion of
the applied electric field to flow
through them.
 VB and CB overlapped or minimum
gap.
 They have large no. of mobile
charge carriers or free electrons
which carry electric current.
 When temperature of conductors
increased, conductivity decreases
and its resistivity increases, because
due to thermal agitation positive
part also starts to move which
retards the motion of mobile
electrons.
 Because their resistivity increases
on rising the temp. thus they have
positive temperature coefficient of
resistance.
 For eg. Cu, Ag, Al, Au etc.
Insulators:
 Insulators are materials
having bad electrical
conductivity,
𝝈 < 10-8
S/cm
(like diamond: 10-14
S/cm).
 They do not practically allow
the electric circuit to flow
through them.
 Large gap between VB and
CB.
 Tthey have very high
resistivity because they have
no charge carriers or free
electrons to carry electric
current.
 E.g. Glass, quartz, rubber,
bakelite etc.
Semi- conductors:
 Semi- conductors are those solids
which are perfect insulators at
absolute zero, but conduct electricity
at room temperature.
 Semiconductors have a
conductivity, 𝝈 between 10-8
S/cm
(insulators) and 103
S/cm
(conductors) (for silicon it can
range from 10-5
S/cm to 103
S/cm);
 Semi-conductors allow a portion of
electric current to flow through them.
 On increasing the temperature of a
semiconductor, its resistivity
decreases or conductivity increases.
 At higher temp, a semiconductor
conducts better. Thus, the
semiconductors have negative temp
coefficient of resistance
 Moderate gap between VB and CB
 Si, Ge, As, Ga etc.

2. JFC Properties of Solids By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
Semiconductors
Extrinsic
Semiconductors
n- type
Semiconductors
p- type
Semiconductors
Intrinsic
Semiconductors
Fermi Level Energy, Ef –
“The hypothetical energy level, where the probability of movement of e-
at the starting of the conduction is maximum. “
Intrinsic semiconductor- On increasing T ; Ef increases.
p- type semiconductor- On increasing T ; Ef increases.
n- type semiconductor- On increasing T ; Ef decreases.
Valence Band Valence Band
n-type p-type
Intrinsic semi- conductors
(Semi-conductors due to thermal agitations)
 At zero Kelvin pure substance silicon and
germanium act as insulators because
electrons fixed in covalent bonds are not
available for conduction.
 But at higher temperature some of the
covalent bonds are broken.
 To break a covalent bond in the crystal
lattice, a certain amount of energy is
required. For e.g. Energy for Ge is 0.72eV,
for Si 1.12eV and for Ga 1.3 eV.
 After breaking the covalent bond electrons
are released and become free to move in
the crystal and thus conduct electric
current.
 This type of conduction is known as
intrinsic conduction as it can be introduced
in the crystal without adding an external
substance.
Extrinsic semi-conductors:
(Semi-conductors due to impurity defects)
 Pure semiconductors have small conductivity
at room temp. therefore, they are not of much
use.
 By adding some amount of impurity atoms to
a pure semiconductor, we can change its
conductivity or characteristics.
 The process of adding impurity to a pure
semiconductor is called “doping”.
 On adding impurities, either the no. of
electrons or holes increases.
 A doped semiconductor is called “extrinsic
semiconductor”.
 Types of extrinsic semiconductors,
 N – type semiconductor
 P – type semiconductor
 When impurity of next group is added, a free
electron gives rise to the conductivity forming
n-type semiconductors.
 Examples- when group 15 elements are
mixed with the crystal of group 14 elements,
or when group 14 elements are mixed with
the crystal of group 13 elements.
 When impurity of previous group is added, a
hole gives rise to the conductivity forming
p-type semiconductors.
 Examples- when group 13 elements are
mixed with the crystal of group 14 elements,
or when group 14 elements are mixed with
the crystal of group 15 elements.
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3. JFC Properties of Solids By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
Ferro-
magnetism
Below Tc, spins are
arranged parallel in
magnetic domains.
Anti-
ferromagnetism
Below TN, spins are
arranged anti-parallel
in magnetic domains.
Ferri-magnetism
Below Tc, spins are
arranged anti-parallel
in magnetic domains,
but do not cancel out
completely.
2. Magnetic Properties of Solids
 The magnetic properties of different materials are studies in terms of their magnetic moments which arise due to the
orbital motion as well as spinning of the electron.
 As electron is charged particle, the circular motion of the electric charge causes the electron to act as a tiny electro
magnet.
 Magnetic moment is a vector quantity and it is represented by μ.
 Bohr Magneton (B.M.) is the fundamental unit of magnetic moment.
 μ(spin only) = √ ( ) B.M. where n is no. of unpaired electrons.
 Due to the magnetic moment of the electrons different substances behave differently towards the external applied
magnetic field.
 Based on the behaviour in the external magnetic field, the substances are divided into different categories as explained
below.
v
(i) Diamagnetic substance:
 Substances which are weakly repelled
by the external magnetic fields,
 Diamagnetic substances have all their
electrons paired.
 Net magnetic moment zero.
 e.g. TiO2, NaCl, benzene etc.
(ii) Paramagnetic substances:
 Weakly attracted by external
magnetic field,
 They have unpaired electrons in their
atoms, ions or molecules,
 Magnetic moments are distributed in
all the direction.
 The paramagnetic substances lose
their magnetism in the absence of
magnetic field.
 e.g. TiO, VO2 and CuO, O2, Cu+2
,
Fe+3
etc.
(iii) Ferromagnetic substances:
 It is a domain property.
 They are strongly attracted by a
magnetic field.
 Such substances remain permanently
magnetised, once they have been
placed in magnetic field, even in the
absence of the magnetic field.
 This type of magnetism arises due to
spontaneous alignment of magnetic
moment of unpaired electrons in the
same direction.
 e.g. Fe, Co, Ni, gadolinium,
CrO2 etc. show Ferromagnetism.
(iv) Anti-Ferromagnetic
substances:
 It is a domain property.
 Substances which are expected to
possess paramagnetism or
Ferromagnetism on the basis of
unpaired electron but actually they
possess zero net magnetic moment
are called anti Ferromagnetic
substances
 Anti-Ferromagnetism is due to
presence of equal number of magnetic
moments in the opposite direction.
 e.g. MnO, Mn2O3, MnO2.
(v) Ferrimagnetic substances:
 It is a domain property.
 Substance which are expected to
possess large magnetism on the basis
of the unpaired electrons but actually
have small net magnetic moments are
called Ferrimagnetic substances
 Net magnetic moment is non-zero.
 e.g. ferrites, magnetic garnets,
magnetite ( Fe3O4)
Curie temperature, TC-
The temperature at which a
ferromagnetic substance
behaves like paramagnetic
substance. It is because of the
unlocking of magnetic domains.
The Néel temperature, TN-
The temperature above which
an antiferromagnetic
Material becomes
paramagnetic
(H) is Direction of Applied
Magnetic Field
(H)
(H)

4. JFC Properties of Solids By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
3. Dielectric properties
 A dielectric substance is, in which an
electric field gives rise to no net flow of electric
charge.
 Because electrons in a dielectric
substance are tightly held by individual atoms.
 But when electric field is applied,
Polarization takes place i.e. nuclei are
attracted to one side and the electron cloud to
the other side.
 The alignment of these dipoles may
result in the net zero dipole moment or it may
have a non-zero net dipole moment.
 The non-zero net dipole moment leads
to certain characteristic properties to solids.
Piezoelectricity
(or pressure electricity):
Pyroelectricity
(or heat electricity):
Ferroelectricity: Anti
Ferroelectricity:
 When mechanical stress (pressure)
is applied on crystals so as to
deform them, electricity is produced
due to displacement of ions.
 The electricity thus produced is
called piezoelectricity and the
crystals are called piezoelectric
crystals.
 If electric field is applied to such
crystals, atomic displacement takes
place resulting into mechanical
strain. This is sometimes
called Inverse piezoelectric effect.
 The crystals are used as pick – ups
in record players where they
produce electrical signals by
application of pressure.
 They are also used in microphones,
ultrasonic generators and sonar
detectors.
 Examples of piezoelectric crystals
include titanates of barium and
lead, lead zirconate (PbZrO3),
ammonium dihydrogen phosphate
(NH4H2PO4) and quartz.
 Crystals which
produce small amount
of electricity when
heated are known as
pyroelectric crystals.
 The electricity thus
produced is called
pyroelectricity.
 Example-
Tourmaline
(a silicate material)
 In some of the
piezoelectric crystals,
the dipoles are
permanently polarized
even in the absence
of the electric field.
However on applying
electric field, the
direction of
polarization changes.
 All ferroelectric solids
are piezoelectric but
the reverse is not
true.
 Examples- Barium
titanate (BaTiO3),
sodium potassium
tartarate (Rochelle
salt) and potassium
dihydrogen phosphate
(KH2PO4).
 In some crystals, the
dipoles align
themselves
alternately, pointing
up and down so that
the crystal does not
possess any net
dipole moment. Such
crystal are said to be
anti-Ferroelectric
 Example-
Lead zirconate
(PbZrO3)
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