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CHME402 Lecture 4

CHME402 – Materials Chemistry
Solid-State Chemistry: Amorphous State
by Dr. Aishuak Konarov
Sol–Gel Processing
Cementitious Materials
Ceramics Processing
Important Materials Applications I: Fuel Cells
Biomaterials Applications
Solid-State Case Study I: Solid Electrolytes for Energy
Storage Applications
Solid-State Case Study II: Porous Materials: Zeolites
and Metal-Organic Frameworks (MOFs)
Dr. Aishuak Konarov
The Amorphous State
There are two other classes of materials that exhibit an amorphous structure, that our society is
indebted to for countless applications – glasses, ceramics, and cementitious materials. Although the
majority of ceramic materials exhibit an amorphous structure when synthesized at low temperatures,
these materials are converted to crystalline phases as their temperature is increased, a process
referred to as annealing.
This results in a ceramic material that is extremely hard with a high melting point, desirable for
structural applications or those occurring within extreme environments such as high temperatures
and/or pressures.
In this lecture, we will describe some important classes of amorphous glasses, ceramics, and cement
with a particular focus on the conditions required for, and structural implications of, their conversion to
a well-ordered array.
Dr. Aishuak Konarov
Sol-Gel Processing
Most are low-temperature methods, often referred to as chimie
douce or soft chemistry methods, although final firing at high
temperature may be needed, especially for ceramic products.
The sol–gel (solution-gelation) process is a versatile solutionbased technique for fabricating ceramic and glassy materials.
In general, sol–gel involves the formation of a sol
(colloidal suspension of ca. ≥200 nm solid particles)
and subsequent crosslinking to form a viscous gel.
The first stage is to prepare a homogeneous solution containing
all the cationic ingredients in the desired ratio. The solution is
gradually dried and, depending on the species present, should
transform to a viscous sol containing particles of colloidal
dimensions and finally to a transparent, homogeneous, amorphous
solid known as a gel, without precipitation of any crystalline phases.
The gel is then fired at high temperatures to remove volatile
components trapped in the pores of the gel or chemically bonded
hydroxyl and organic side-groups and to crystallise the final product.
Illustration of the products obtained through sol–gel processing
Dr. Aishuak Konarov
Sol-Gel Processing
First, organometallic precursors, particularly alkoxides, are widely used for the small-scale synthesis of known
or new materials, often containing several different cations.
The reagents for alkoxide-based sol–gel syntheses are metal–organic compounds:
- tetraethyl orthosilicate (TEOS), Si(OCH2CH3)4, as a source of SiO2,
- titanium isopropoxide, Ti(OiPr)4, as a source of TiO2,
- aluminium butoxide, Al(OBu)3, as a source of Al2O3.
These covalent liquids are mixed in the appropriate ratios, often with an alcohol to promote miscibility of the
alkoxide and H2O. Water is a key reagent since it hydrolyses the alkoxides, usually in the presence of either acid
or base as a catalyst to speed up reaction
Hydrolysis occurs in two steps:
(i) replacement of –OR groups by –OH, e.g.
Si(OCH2CH3)4 → Si(OCH2CH3)3OH + Si(OCH2CH3)2(OH)2 + etc.
(ii) condensation polymerization with elimination of H2O, e.g.
(RO)3Si–OH + HO–Si(OR)3 → (RO)3Si–O–Si(OR)3
The composition, structure and viscosity of the reaction products depend very much on the degree of hydrolysis/condensation;
careful control of the reaction variables is required to achieve the desired product. For the synthesis of complex oxides
containing more than one cation, M, M’, cross-condensation is required:
{–M–OH + HO–M’–} → {–M–O–M’–}
and it is essential to achieve this instead of condensation of the components separately.
Hydrolysis may be base catalysed, with nucleophilic substitution of OH−:
HO− + Si(OR)4 → (HO)Si(OR)3 + RO−
or acid catalysed, with electrophilic attack by H+ (or H3O+):
Cl− + H+ + ROSi(OR)3 → HOSi(OR)3 + RCl
The final stage of synthesis is to heat, or calcine, the gel, to decompose organic matter and leave an oxide product.
Dr. Aishuak Konarov
Sol-Gel Processing
In general, silicon oxide networks obtained via acid-catalyzed conditions consist of linear or randomly
branched polymers; by contrast, base-catalyzed systems result in highly branched clusters
Comparison of the morphology with the pH of the sol–gel process.
It is important that the water be removed prior to the
drying event. This is easily accomplished through soaking
the alcogel in pure alcohol.
The soaking time is dependent on the thickness of the
gel. Any water left in the gel will not be removed by
supercritical drying, and will lead to a dense, opaque
Similarly, water will not be removed as readily as alcohol
by simple evaporation; hence, water-containing gels will
result in heavily cracked and heterogeneous xerogels.
Dr. Aishuak Konarov
Aerogels retain the original shape and
volume of the alcogel, typically >85%
of the original volume. By contrast,
xerogels exhibit significant shrinking
and cracking during drying, even under
room-temperature conditions
From drinking vessels and windows to eyeglass lenses, materials comprising glass have long played an
important role in our society. In fact, it is estimated that applications for glass date back to Egypt in ca.
3500 BC. Although we are most familiar with transparent silica-based (SiO2) glass (Fig below), there are
many other types of glass that may be fabricated for various applications.
By definition, the term glass refers not a specific material, but a general architectural type—an
amorphous solid that has cooled to rigidity without crystallizing.
Glasses are most commonly made by rapidly quenching a melt; accordingly, the constituent atoms are
not allowed to migrate into regular crystalline lattice positions.
Infrared-transmitting chalcogenide
glasses such as As2E3 (E = S, Se, Te)
are suitable for specialized
applications such as optical storage,
sensors, and infrared lasers.
Molecular structure of amorphous SiO2, comprised
of randomly corner-linked SiO4 tetrahedra
Dr. Aishuak Konarov
It is noteworthy to point out why a material as disordered as glass is transparent.
That is, one would think that the amorphous structure of glass should facilitate opacity, which is the extent to which
visible radiation is blocked by the material it is passing through.
If we think about single crystals, these will appear translucent if the lattice spacings are smaller than the visible
range of wavelengths (ca. 300–700 nm). By the same measure, glass also appears transparent since the degree of
disorder actually covers a distance less than a wavelength of visible light (Rayleigh scattering).
There are two primary rationales for the transparency of glass: electronic and structural.
1) as we will see shortly, glass may contain a variety of dopants that will afford particular colors (via electronic
transitions) or physical properties (e.g., enhanced hardness, thermal/electrical conductivity, reflectivity, etc.).
However, these impurities are only present in sufficient quantity to cause only partial absorption of the
electromagnetic spectrum, resulting in observable transparency—although less pronounced relative to
undoped glass.
2) unlike metals, glasses are held together by covalent and/or ionic bonding and do not contain free electrons in
their structure. Accordingly, the incident wavelengths are not perturbed into destructive waves and are free to
transmit through the material. Additionally, the degree of disorder within glasses is the same order of
magnitude as the incident radiation, allowing the light to pass through relatively unattenuated. However, if the
glass contains imperfections, and/or inclusions of metals or larger particles, it will become increasingly opaque.
Dr. Aishuak Konarov
Glasses and ceramics are largely based on a covalently bound network that is comprised of an infinite array of
silicate (SiO44-) tetrahedra.
A variety of structures are possible by Si-O-Si linkages among adjacent tetrahedra. Since the silicate sub-units
carry an overall 4 charge, alkali or alkaline earth metal ions are commonly present in order to afford charge
neutrality, and link adjacent silicate tetrahedra via ionic bonding.
Molecular structures of common silicate anions. (a) SiO44-, (b)
Si2O76-, (c) Si6O1812-, and (d) a metasilicate polymer chain {SiO32-}
Dr. Aishuak Konarov
Schematic representation of
ionic positions within soda glass.
The most straightforward method to make silica (SiO2) glass, known as fused silica or quartz glass, is through
melting sand at a temperature of 1800–2000 °C followed by very slow cooling. Unlike other glasses that require a
rapid quenching event, quartz will automatically form a glassy solid at all but the slowest cooling rates—a
consequence of its complex crystal structure.
For example, it is estimated to have taken 100,000 years to form natural crystalline quartz!
Crystalline silica exists as three varieties, with each form having slightly differing crystal structures
and physical properties:
Two methods commonly used to synthesize crystalline quartz are hydrothermal (autoclave at high
temperature/pressure, containing water and seed crystals) and flux growth.
LiO, MoO, PbF2 and silica powders are added to a crucible; the ionic compounds serve as a molten solvent
to dissolve materials with a high melting point, facilitating crystallization at lower pressures/temperatures.
Fused silica is thermally stable at temperatures up to ca. 1,665◦C.
Dr. Aishuak Konarov
The chemistry of glass making is now a mature field, with many types available for a variety of applications. In
order to decrease the prohibitively high melting point of SiO2, ca. 18% of sodium carbonate (“soda,” Na2CO3)
is often added to sand, resulting in a silica framework doped with Na+ ions.
The resultant glass is more easily workable than fused silica due to interruption of the silicate network.
However, the sodium ions are detrimental since they are easily solvated by water, which leads to corrosion.
To prevent such weathering, ca. 10% of limestone (CaCO3) is added to effectively replace the Na+ ions with
Ca2+. When this mixture is heated to its melting point (ca. 1000 °C), a mixture of calcium silicate (CaSiO3)
and sodium silicate (Na2SiO3) results. Upon cooling, the most prevalent type of glass, called “crown glass”
or soda–lime glass, is generated.
This type of glass accounts for over 90% of the glass used worldwide.
a With
average particle diameters of ca. 50–100 nm
Dr. Aishuak Konarov
The chemistry of glass making is now a mature field, with many types available for a variety of applications. In
order to decrease the prohibitively high melting point of SiO2, ca. 18% of sodium carbonate (“soda,” Na2CO3)
is often added to sand, resulting in a silica framework doped with Na+ ions.
The resultant glass is more easily workable than fused silica due to interruption of the silicate network.
However, the sodium ions are detrimental since they are easily solvated by water, which leads to corrosion.
To prevent such weathering, ca. 10% of limestone (CaCO3) is added to effectively replace the Na+ ions with
Ca2+. When this mixture is heated to its melting point (ca. 1000 °C), a mixture of calcium silicate (CaSiO3)
and sodium silicate (Na2SiO3) results. Upon cooling, the most prevalent type of glass, called “crown glass”
or soda–lime glass, is generated.
This type of glass accounts for over 90% of the glass used worldwide.
a With
average particle diameters of ca. 50–100 nm
Dr. Aishuak Konarov
Another interesting application for glasses is for light control, referred to as “smart glass.” We are all familiar with
movie scenes where a top-secret meeting takes place, and a flip of the switch instantly darkens or clouds the
windows. More routinely, it is now commonplace to have self-dimming mirrors that react to trailing vehicle headlights.
Three main technologies are responsible for these intriguing materials applications:
photochromic glasses, electrochromic devices (ECDs), and suspended-particle devices (SPDs).
Photochromic glasses exhibit a darkening effect upon exposure to particular wavelengths
(usually in the UV regime) of light, and date back to the work of Corning in the 1960’s. The
darkening effect results from redox reactions involving microcrystalline metal halides (e.g.,
AgCl, CuCl) that are present within the glass.
Electrochromic materials change color due to an injection of electrons. The typical ECD
has a variety of layers, sandwiched between glass. When no voltage is applied to the
device, the incoming light will pass through undisturbed (ca. 70–80% transmittance).
SPDs operate through the behavior of rod-like
particles (e.g., liquid crystals) toward an applied
voltage. When no voltage is applied, the
particles are randomly aligned, and do not
allow light to pass through the device.
However, an electric charge will polarize the
particles to align with the field.
Dr. schematic
Aishuak Konarov
of an (a) electrochromic device and (b) suspended-particle device
Cementitious Materials
The use of cementitious materials for structural applications
dates back to ancient Egypt.
A type of cement was used to hold together the limestone
blocks of the great pyramids that still stand today.
During the time of the Roman Empire, an improvement of
cement formulations was developed, which used a finely
divided volcanic ash, known as Pozzolana, found in various
parts of Italy.
Although they did not realize it at the time, the hardening process
occurred due to the reaction of the aluminosilicate-based ash with
Ca(OH)2 in the presence of water to yield a calciumsilicate-hydrate
(CSH) rigid gel.
Amazingly, thousands of years later, the CSH structure is not yet
completely understood; it is likely a disordered form of the hydrated
calcium silicate mineral tobermorite
Dr. Aishuak Konarov
Cementitious Materials
The last major development in cement technology occurred in the early nineteenth century in
England. Bricklayer Joseph Aspdin first made a variety of cement known as Portland cement—
not in a laboratory, but on his kitchen stove! His patent in 1824 changed the world forever, as
this form of cement is the basic ingredient in concrete—essential for the erection of virtually all
buildings and many roads throughout the world. In fact, concrete is the most heavily used manmade material.
As of 2017, it is estimated that the worldwide annual production of concrete amounts to 3 tons
for every man, woman, and child on earth—second only to water in terms of human
It is interesting to note the developmental timeline for
cement/concrete, which has addressed many important
societal needs. For example, if we consider road
construction, stones were used as early as 4000 BC,
and were still prevalent in early America—still evident in
some historical cities such as Boston, MA.
Cross-section representation of a powdered cement particle. Dicalcium silicate (Ca2SiO4),
tricalcium silicate (Ca3SiO5), tricalcium aluminate (Ca3Al2O6), and tetracalcium aluminoferrite
(Ca4AlnFe(2-n)O7) crystallites are abbreviated as C2S, C3S, C3A, and C4AF, respectively.
Dr. Aishuak Konarov
Cementitious Materials
Portland cement is produced from the sintering of minerals containing CaCO3, SiO2, Al2O3, Fe2O3, and
MgO in a ceramic kiln, held at a temperature of ca.1500 °C.
Equations 2.27, 2.28, 2.29, 2.30, and 2.31 show the reactions that occur during the processing of
The resulting complex material is referred to as clinker, and may be stored for many years under
anhydrous conditions before its use in concrete.
It is estimated that Portland cement manufacturing accounts for over 5% of the world’s total emission of
CO2. As a result, there is an increasing focus on using additives, such as fly ash
(a by-product from coal-fired power plants).
When water is mixed with Portland cement, the product sets in a few hours and hardens over a period of
3–4 weeks. The initial setting process is caused by the reaction between water, gypsum (CaSO42H2O,
added to clinker to control the hardening rate), and C3A forming calcium and aluminum hydroxides.
Dr. Aishuak Konarov
Ceramics Processing
There are three categories of (semi) crystalline ceramics: oxides (e.g., alumina, zirconia), nonoxides (carbides, borides, nitrides, silicides), and composites of oxides/non-oxides.
Perhaps the least sophisticated, but most widely used, means for ceramics processing involves solidstate reactions, known as “shake ‘n bake”.
This is the method-of-choice for most commercial syntheses of ceramics, consisting of a hightemperature multi-step process involving:
(i) Grinding/milling - Powders must be finely divided in order to maximize their surface area and rate of
diffusion. As an alternative to “top-down” pulverization, “bottom-up” methods such as co-precipitation from
solution (e.g., sol-gel), gas-phase pyrolysis, spray-drying, or freeze-drying are also commonly used to prepare
ceramic precursor powders.
(ii) Mixing and forming - the powder is mixed with water to semi-bind the particles together, and is cast, pressed,
or extruded into the desired shape. This step is critical to enhance the intimate contact of reactant particulates
while minimizing direct contact with the crucible, which may introduce impurities.
(iii) Drying - the material is heated at temperatures >200°C to remove the water or organic binder(s) and
lubricant(s) from the formed material. Care must be used to prevent rapid heating, to prevent cracking and other
surface defects.
(iv) Firing/sintering - quite often, precursor compounds at earlier stages of ceramic processing are at least
partially amorphous. The final firing/sintering stage is used to fuse the particles together and convert the material
into a (poly)crystalline product, which has the bulk form and physical properties desired for a particular application.
For instance, ceramic refractories such as silica (1160°C), alumina (2200°C), or zirconia (2300°C), as well as
noble metals such as Pt (1770°C), Au (1063°C), Ir (2450°C), Ta (3020°C), or W (3422°C) are often used.
Dr. Aishuak Konarov
Material Preparation Methods
Many methods can be used to synthesize non-molecular inorganic solids. Some
solids can be prepared by a variety of routes but others, especially those that are
not thermodynamically stable, may be much more difficult to prepare and may
require special methods.
 Solid-state
 Solution techniques (Sol-gel, hydrothermal, spray pyrolysis, other precipitation
Non-molecular inorganic solids can also be prepared in various forms, as fibers,
films, foams, ceramics, powders, nanoparticles and single crystals, as shown for
one example, Al2O3, in Table below.
Dr. Aishuak Konarov
Solid State Reaction or Shake ’n
Bake Methods
 The oldest, simplest and still most widely used method to make inorganic
solids is to mix together powdered reactants, perhaps press them into pellets
or some other shape and then heat in a furnace for prolonged periods.
 The method is not sophisticated, hence the use of alternative names such as
shake ’n bake or, beat ’n heat! It is nevertheless very effective and, for
instance, almost all the high-Tc superconductors were first prepared by this
 Solid state reactions are intrinsically slow because, although the reactants
may be well mixed at the level of individual particles (e.g. on a scale of 1 μm
or 10-3 mm), on the atomic level they are very inhomogeneous.
 In order to achieve atomic level mixing of reactants, either solid state counter
diffusion of ions between different particles or liquid- or gas-phase transport
is necessary to bring together atoms of the different elements, and in the
correct ratio, to form the desired product.
Dr. Aishuak Konarov
Solid State Chemistry and its Applications,
2nd Edition, Anthony R. West
Solid State Reaction: Example
Consider a typical solid-state reaction, that of MgO and Al2O3 powders to form
MgAl2O4 spinel. Let us consider the various processes involved in the reaction
Reaction rate is
extremely slow in
RT, probably it
would take 1M
In practice, the
reaction occurs
above 1200 ºC.
Idealised reaction mixture composed of grains of MgO and
Al2O3. In practice, their shapes will be irregular, of different
size and not arranged in such an orderly fashion. Solid State Chemistry and its
Dr. Aishuak Konarov
Applications, 2nd Edition, Anthony R.
Nucleation and growth
After appropriate heat treatment, the crystals have
partially reacted to form a layer of MgAl2O4 at the
The first stage of reaction is the
formation of MgAl2O4 nuclei.
This nucleation is rather difficult:
- The considerable difference in
structure between reactants and
- The large amount of structural
reorganization that is involved in
forming the product: bond must be
broken and reformed and atoms
must migrate.
the first few atomic layers of product nuclei may form easily,
thickening of the product is more difficult
Nucleation and growth
MgO + Al2O3 --> MgAl2O4
Dr. Aishuak Konarov
Solid State Chemistry and its Applications,
2nd Edition, Anthony R. West
Synthesis of MgAl2O4
The spinel formation reaction is particularly slow because ions such as Mg2+
and Al3+ diffuse very slowly; typically, heating for 1 week at 1500 ºC would be
required to form a fairly pure spinel product.
Important factors that influence the rate of reaction between solids:
Defects in both reactants and product are required, particularly, vacant sites for
adjacent ions to hop into. High temperatures are therefore required so that ions have
sufficient thermal energy to, occasionally, hop out of one site into an adjacent
vacancy or interstitial site.
Consequently, it can be difficult for solid state reactions to proceed to completion
once the remaining reactants are well separated from each other. One important
way to accelerate reactions is to grind the partially reacted mixtures, so as to break
up reactant/product interfaces and bring fresh reactant surfaces into contact.
Another way is if gas- or liquid-phase assisted transport of matter can occur and
bring reactants together without the need for long-range solid-state diffusion. A small
amount of liquid or gaseous transporting agent may be very effective in enhancing
reaction rates.
Dr. Aishuak Konarov
Practical considerations and some
examples of solid-state reactions
 The problems associated with spinel synthesis by solid state reaction are
particularly difficult since both reagents, MgO and Al2O3, are very stable, inert,
non-reactive solids.
 Solid state reactions may be easier if one or more of the starting materials is
chemically reactive and/or contains ions that can diffuse easily.
 Other problems may arise, however, such as potential loss of reactants by
evaporation (e.g. alkali metal oxides, Tl2O, PbO, Bi2O3, HgO), or reactivity
towards the container (e.g. transition metal-containing materials).
With care, and attention to synthesis procedures, these problems can usually be
avoided. There are four main issues for consideration in planning a solid-state
 choice of starting materials
 mixing method
 container
 heat treatment conditions
Dr. Aishuak Konarov
Choice of starting materials
 Ideal starting materials should be of accurately known stoichiometry, pure and
reactive. Problems with stoichiometry and purity can arise if the reagents are
sensitive to water and/or CO2 in the atmosphere or contain transition elements in
uncertain or mixed valence states. Reagents may need to be dried, at a
temperature found by trial and error, and subsequently kept in a desiccator.
 For oxide synthesis, it can be useful to use oxy salt reagents, such as carbonates,
acetates or nitrates (but not sulfates, which are very stable thermally), since these
decompose during the initial stages of reaction on heating. This decomposition step
may decrease greatly the particle size of the reagent, increase its surface area and
therefore increase its potential reactivity. In addition, evolution of gases during the
decomposition can help to mix the solid reactants.
For synthesis of MgAl2O4:
Starting materials: MgO and Al2O3. These should be dried thoroughly prior to
weighing, especially MgO which is hygroscopic, by heating at high temperature ,
e.g. 200 to 800 ºC, for few hours.
MgCO3 (or some other oxysalt of magnesium) could be used as the source of
MgO since it is less hygroscopic than MgO.
Fine grained materials should be used if possible in order to maximize surface
areas and hence reaction rates.
Dr. Aishuak Konarov
Mixing methods
 The mixing can be done manually using a mortar and
pestle (agate mortars and pestles are useful since they
are non-porous, readily cleaned and should not
contaminate samples); there are also various laboursaving mechanical mixing techniques such as ball
milling, in which the mixture of reactants is placed
inside a rotating container together with a number of
balls of, for instance, agate.
 The container is then rotated for a period of time, e.g. 3–24 h, and the effect of the
tumbling motion with the agate balls is to reduce the average particle size of the
reactants in addition to achieving an intimate mixture. High-energy milling is
possible in planetary ball mills, which are rotated at very high speed.
 While the mixing and milling processes are carried out rapidly and effectively,
there is a danger of contamination from the milling media. To facilitate mixing, by
whatever method, a liquid such as water or an organic liquid is often added and
then needs to be removed by drying at the end of the mixing stage.
Dr. Aishuak Konarov
If atmospheric sensitivity of the desired product phase is not a problem, the
reaction mixture can simply be heated in air in a furnace in a suitable container.
Prime consideration for the container is that it should not react with the sample.
Frequently-used inert containers for oxides are boats or crucibles of
Pt (but Pt reacts with Li2O, BaO and many transition metal oxides).
Au (but its melting temperature, 1063 ºC, places an upper limit on the reaction
temperatures that may be used; however, Au is generally more inert than Pt).
Al2O3 (high-purity alumina is inert and high melting, but nevertheless contamination
from the reactants may occur).
SiO2 glass (crucibles of pure SiO2 glass can withstand temperatures up to 1200 ºC
before the glass softens and starts to devitrify; oxides of alkali metals, in particular,
are reactive towards SiO2).
Graphite crucibles are commonly used as containers for the synthesis of sulfides,
other chalcogenides and nitrides.
Dr. Aishuak Konarov
Heat treatment conditions
The heating schedule should be designed to
(a) cause smooth decomposition of any oxy salt reagents without excessive frothing,
melting or leakage of reagent from the container,
(b) avoid melting and in particular volatilization of one or more of the reagents and
(c) apply temperatures at which the reagents react together on a reasonable timescale
(e.g. 12–24 h).
Reactions may be carried out in air or, if a tube furnace is available, a range of
controlled atmospheres may be used. Alternatively, sealed ampoules of silica glass or
precious metals may be used to prevent loss of volatile reagents or atmospheric attack.
For known materials, there may be recipes in the literature detailing appropriate reaction
conditions, but for the attempted synthesis of new materials, a trial and error approach
is usually needed.
In the synthesis of phase containing Fe2+, reduction atmosphere is
necessary to prevent oxidation to Fe3+.
Dr. Aishuak Konarov
Li4SiO4 is the parent phase for a family of Li+ ion conductors that can be
prepared by the reaction:
Problem: Li2CO3 melts and decomposes readily above ∼720 ◦C; it is reactive
towards most container materials, including Pt and silica glass.
Solution: Use Au containers; carry out decomposition and pre-reaction of
Li2CO3 at ∼650 ºC for a few hours before final firing at 800–900 ºC overnight.
Dr. Aishuak Konarov
YBa2Cu3O7, YBCO, is the classic 90 K superconductor. It can be prepared by the
BaCO3 is particularly stable on heating and it can be difficult to remove the last
traces of CO2 during reaction. Also, many materials, such as YBCO, may react
slowly with atmospheric CO2 causing a partial reversal of the reaction used in the
(ii) CuO is reactive to most container materials at high temperatures.
(iii) The oxygen content 7 – δ of the YBCO product is variable and must be controlled to
optimize Tc.
React in a CO2-free atmosphere, with Ba(NO3)2 as a source of BaO.
(ii) Make pellets of reaction mixture [after decomposition of Ba(NO3)2] and react these
on a bed of pre-prepared YBCO.
(iii) After reaction at ∼950 ºC, carry out final heating at ∼350 ºC to allow O2 uptake to
occur and achieve the desired stoichiometry YBa2Cu3O7.
Dr. Aishuak Konarov
Na β/β̋ -alumina is the classic Na+ ion-conducting solid electrolyte. In reality,
there are two Na aluminate phases whose formulae are written ideally as
NaAl11O17 (β) and NaAl5O8 (β̋), although both phases form solid solutions with
variable Na:Al ratios. They can be prepared as follows:
Problem: Na2O is volatile at the required reaction temperatures; lower temperatures
cannot be used because of the inertness and unreactivity of Al2O3.
Carry out pre-reaction at 700–800 ºC and expel CO2; fabricate ‘green’ pellets or
tubes of the partially-reacted mixture; cover the pellets or tubes with pre-reacted
β/β̋ -alumina and fire at 1400–1500 ºC. This ‘buffering’ prevents significant loss of
Na2O from the samples at high temperatures.
(ii) Use high surface area, reactive alumina starting materials such as boehmite or γ Al2O3. These have a defect spinel structure (similar to that in the β/β̋ -alumina
product) and the first stage of reaction involves intercalation of Na+ into the
particles of alumina.
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Video source: VidLib
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Hydrogen fuel cell vehicles
Toyota Mirai
Hyundai Nexo
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Supercapacitors feature high power
densities and may quickly release their
stored energy.
In contrast, both fuel cells and batteries
feature relatively high energy densities that
generate electricity more slowly via
chemical reactions that occur at the
positively charged (cathode) and
negatively charged (anode) electrodes.
As opposed to batteries that store a limited
amount of energy, fuel cells operate with a
continuous fuel flow that allows prolonged
periods of electricity generation.
In addition, these systems may be easily scaled-up to power large electrical grids.
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
An electrolyte is an essential component within
energy-storage devices, used to facilitate the
selective migration of ions between the electrodes.
For batteries, the electrolyte is liquid-based,
composed of organic solvents such as ethyl
carbonate, methyl carbonate, or propylene
Although liquid electrolytes offer benefits of high conductivity and electrode wetting,
they often suffer from thermal and electrochemical instabilities.
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
In general, solid electrolytes must have the following characteristics:
 High ion conductivity
 Low volatility and flammability
 Stability in both oxidizing and reducing environments
 Chemical compatibility with other cell components
 High density to prevent mixing of fuel and oxidant gases (fuel cells)
 Desirable thermal expansion properties, to prevent cracking of the
device at high temperatures
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Fuel Cell
Ascent, Japan Railway Technical
Research Institute, pp. 20–21, 2016
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
Fuel Cell Electrolyte
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
All Solid State Battery
The design of solid-state electrolytes for rechargeable batteries began in the 1980s, with the
development of a variety of Li-ion conductive polymers such as poly(acrylonitrile) (PAN) and
poly(vinylidene fluoride) (PVDF).
Inorganic-based solid electrolytes such as lithium phosphorus oxynitride (LiPON) were
developed in the 1990s, which showed better ion conductivity and less issues with potential
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
All Solid State Battery
Today, most work focused on the development of inorganic-based solid electrolytes,
which may be grouped into five main categories:
� space group; e.g., Li3xLa2/3-x[ ]1/3-2xTiO3, where [] are
 Perovskite-type (Pm3m
vacancies created by aliovalent doping of Li+ ions into La3+ sites)
 Lithium superionic conductor (LISICON)-type (Pnma space group; e.g.,
Li3+x(P1-xSix)O4, Li10MP2S12 (M = Si, Ge, Sn), Li11Si2PS12)
� space group; e.g.,
 Sodium superionic conductor (NASICON)-type (R3c
L1+6xM4+2-xM’3+x(PO4)3 (L = Li, Na; M = Ti, Ge, Sn, Hf, Zr; M’ = Cr, Al,
Ga, Sc, Y, In, La))
 Argyrodite-type (F4� 3m space group; e.g., Li6PS5X (X = Cl, Br, I))
 Garnet-type (Ia3� d space group; e.g., Li5La3M2O12 (M = Nb, Ta), Li6ALa2M2O12
(A = Ca, Sr, Ba; M = Nb, Ta), Li5.5La3M1.75B0.25O12 (M = Nb, Ta; B = In, Zr),
Li7La3Zr2O12, Li7.06M3Y0.06Zr1.94O12 (M = La, Nb, Ta)
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
All Solid State Battery
The diffusion of an ion within a crystalline solid may only proceed if sufficient energy is provided
to overcome the activation energy (also known as the “migration energy”) that separates two
crystallographic sites —typically interstial or vacant sites in the lattice.
As the valency of the migrating cation increases, the activation energy of its migration will
increase due to enhanced electrostatic attractions between the surrounding lattice counterions
(e.g., O2-, S2-, Cl-, PO43-, etc.). Hence, as a general rule, monovalent cations (e.g., Li+, Na+, K+,
etc.) will exhibit the highest diffusion coefficients and lowest migration energies than divalent
(e.g., Mg2+, Ca2+, Zn2+, etc.) or trivalent (e.g., Al3+) species.
For ions of the same valency, such as Li+ and Na+, the smaller ion (Li+) will generally move
more efficiently through a given crystal lattice. However, the framework lattice also plays a
governing role in ionic migration.
If the diffusing cation is too small for a given lattice site, it will
occupy a large “electrostatic well”, formed from close interactions between the surrounding
lattice counterions.
This will result in slow diffusion due to a high activation energy for its migration. On the other
hand, if the ion is too large for a lattice position, the cation will experience slower diffusion as it
attempts to navigate through the bottlenecks of the lattice framework
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
For satisfactory ion conduction, the crystal
lattice of the solid electrolyte must be
designed to enhance the diffusion coefficient
of the migrating cation.
Not only should there be an excess of
equivalent (or near-equivalent) sites relative
to the number of migrating ions, but these
sites must be connected to form continuous
diffusion channels.
For a given crystal structure, the concentration of migrating ion, as well as frameworksubstitution with ions of differing sizes and valencies will vary the ionic conductivity of the solid
by as much as 5–6 orders of magnitude.
For instance, the ionic conductivity of perovskite-based solid electrolytes is increased from 10-7
to 10-3 S cm-1 as the rare-earth metal is changed from Sm3+ to the larger La3+.
Dr. Aishuak Konarov
Solid-State Case Study I: Solid Electrolytes
for Energy Storage Applications
For garnets with the general formula A3B2(XO4)3, Asites have 8-fold coordination (antiprismatic), B-sites
are octahedral, and X-sites are tetrahedrally
coordinated. In garnets such as Li3Nd3Te2O12, Li+
ions occupy tetrahedral sites exclusively, which limits
the ionic conductivity of the solid (ca. 10-6 S cm-1).
However, aliovalent metal doping to yield structures
such as Li5La3M2O12 (M = Nb, Ta, Sb), Li6ALa2M2O12
(A = Mg, Ca, Sr, Ba; M = Nb, Ta), Li7La3M2O12 (M =
Zr, Sn) feature a much higher Li content, with Li+
ions in both distorted octahedral and tetrahedral
Since the Li+ sites are very well connected within the
garnet structure, an increasing Li content results in
faster Li-ion mobility, up to 10-3 S cm-1
Top: Lithium occupancy in the garnet-type Li5+xLa3xAxM2yByO12 where A = divalent, B = tri- or tetravalent and M = pentavalent
ions, showing three possibilities for Li-ion distribution.
Bottom: The importance in Li-ion placement within octahedral sites (48 g/96 h sites), relative to tetrahedral sites (24d), for
Dr. Aishuak Konarov
enhanced ionic conductivity.
Thank you!