Solid State Chemistry : An Introduction to Crystal Structures

Solid State Chemistry : An Introduction

to Crystal Structures

FMIPA UGM – September 2020

Prof. Dra. Wega Trisunaryanti, M.Si., Ph.D.Eng

Dr.rer.nat Niko Prasetyo

Outline

 Solid state chemistry

 12 chapters from crystal structures to nanoscience  Lecture and reading materials :

 At this classroom

 Ugm.id/1ND

 Final exam

 Open Book (not open google)  Do it by yourself!

 Main reference :

 Solid State Chemistry: An Introduction, Third Edition 3rd Edition by Lesley E. Smart

Crystal characterization

 X-Ray Diffraction (XRD)

 Wilham Conrad Röntgen discovered X-Rays in 1901

 Leading to revolutionary inventions in medical, crystallography, chemistry,

Crystal characterization

Crystal characterization

Atom of the anodematerial electrons Ejected electron (slowed down and changed direction)

Crystal characterization

Crystal characterization

 X-Ray Diffraction (XRD)  Principle of X-Ray

Crystal characterization

energy levels (schematic) of the electrons

Intensity ratios

Crystal characterization

 X-Ray Diffraction (XRD)  Principle of X-Ray

Anode kV Wavelength Filter

Co 7.7 K1 : 1.78890

K2 : 1.79279

K1 : 1.62073

Fe

0.012 mm

Bremsstrahlung = continuous spectra characteristic radiation = line spectra

Crystal characterization

 X-Ray Diffraction (XRD)  Diffractogram

Crystal characterization

 X-Ray Diffraction (XRD)  Diffractogram single crystal

Crystal characterization

 X-Ray Diffraction (XRD)

 Diffractogram powder crystal  low intensity peaks

Crystal characterization

 X-Ray Diffraction (XRD)  Bragg’s Law



Crystal characterization

 X-Ray Diffraction (XRD)  Bragg’s Law



Crystal characterization

 X-Ray Diffraction (XRD)  Bragg’s Law



Crystal characterization

 X-Ray Diffraction (XRD)  Bragg’s Law

 In Bragg’s Law, the missing point is “d” (spacing between crystals)  To calculate d, we have to know the Miller index

 For cubic crystal 

Crystal characterization

 X-Ray Diffraction (XRD)  Bragg’s Law

 Example :

 The results of a x-ray diffraction experiment using x-rays with λ = 0.7107 Å (a

radiation obtained from molybdenum (Mo) target) show that diffracted peaks occur at the following 2θ angles:

Determine the crystal structure, the indices of the plane producing each peak, and the lattice parameter of the material.

Crystal characterization

 X-Ray Diffraction (XRD)  Solution

We can first determine the sin2 _{θ value for each peak, then divide through by the lowest}

Crystal characterization

 X-Ray Diffraction (XRD)  Solution

We could then use 2θ values for any of the peaks to calculate the interplanar spacing and thus the lattice parameter. Picking peak 8: 2θ = 59.42 or θ = 29.71



This is the lattice parameter for body-centered cubic iron. 400

sin

.7107

sin 29.71 .71699

Crystal characterization

 X-Ray Diffraction (XRD)  Applications

 Identification of unknowns and phase purity

 Matching the fingerprints pattern with JCPDS databases  Qualitative analysis

 Powder diffraction can confirm whether two similar compounds, where one

Crystal characterization

 X-Ray Diffraction (XRD)  Applications

Crystal characterization

 X-Ray Diffraction (XRD)  Applications

 Crystallite size

 As the crystallite size decreases, the width of the diffraction peak increases  The Debye-Scherrer formula enables the thickness of a crystallite to be

calculated from the peak widths

Crystal characterization

 X-Ray Diffraction (XRD)  Applications

 Crystallite size

 The Debye-Scherrer formula enables the thickness of a crystallite to be

calculated from the peak widths



where T is the crystallite thickness, λ the wavelength of the X-rays (T and λ have the same units), θ the Bragg angle, and B is the full-width at half-maximum (FWHM) of the peak (radians) corrected for instrumental broadening. (BM and Bs are the FWHMs of the sample and of a standard, respectively

Crystal characterization

 X-Ray Diffraction (XRD)  Applications

 Following reaction mechanisms and phase diagrams

 By collecting an X-ray pattern at regular intervals as the sample is heated

on a special stage in the diffractometer, evolving phases can be seen as new lines which appear

Crystal characterization

 Extended X-Ray Absorption Fine Structure (EXAFS)

 Basic idea : x-ray beam causes core electron to leave the K shell and a

vacancy in core shell is formed. Outer electron will relax and fill the vacancy

 In Extended X-Ray Absorption Fine Structure (EXAFS), X-radiation is

absorbed by a bound electron in a core shell and ejected as a photoelectron. If the absorption coefficient of the sample is measured as a function of the X-ray frequency, a sharp rise, or absorption edge is observed at the K shell threshold energy.

 Each element has its own characteristic K shell energy, and this makes it

possible to study one type of atom in the presence of many others, by tuning the X-ray energy to its absorption edge.

Crystal characterization

 Extended X-Ray Absorption Fine Structure (EXAFS)

(a) The photoelectron is ejected by X-ray absorption

(b) The outgoing photoelectron wave (solid line) is backscattered constructively by the surrounding atoms

Crystal characterization

 Extended X-Ray Absorption Fine Structure (EXAFS)

• EXAFS allows determining the chemical environment of a single element in terms of the number and type of its neighbors, inter-atomic distances and structural

disorders.

• X-rays are very penetrating, so EXAFS, like X-ray crystallography, examines the structure of the bulk of a solid. It has the disadvantage of only providing

information on interatomic distances but has the considerable advantage that it is not confined to crystalline samples, and can be used on amorphous solids,

Crystal characterization

 X-RAY ABSORPTION NEAR-EDGE STRUCTURE (XANES)

• XANES provide valuable information about the oxidation state, coordination environment, and bonding characteristics of specific elements in a sample.

Crystal characterization

 Solid State Nuclear Magnetic Resonance Spectroscopy (MAS NMR)

• In liquid NMR spectroscopy, dipolar interactions and anisotropic effects are averaged out by the molecular motion, but this is not so in the solid state. The NMR spectra of solids tend to be broadened by three main effects:

• Magnetic Dipolar Interactions can be removed by the application of a high-power decoupling field at the resonance frequency

• Sensitivity can be improved by using a technique known as cross

polarization where a complex pulse sequence transfers polarization from

an.

• The chemical shift of a particular atom varies with the orienabundant

nucleus to the dilute spin thereby enhancing the intensity of its signaltation of the molecule to the field which gives a range of values, an effect known as the chemical shielding anisotropy, which broadens the band.

• MAS NMR is often used to imply the application of any or all of these techniques in obtaining a solid state NMR spectrum. MAS NMR has proved very successful in elucidating zeolite structures.

Crystal characterization

 DIFFERENTIAL THERMAL ANALYSIS (DTA)

• DTA measures the temperature difference between a sample and a reference as the temperature is increased.

• The sample and reference material are heated on one furnace and the difference in temperature between the two is monitored and recorded against time.

• Any reaction in the sample will be represented as a peak in the plot of differential temperature; exothermic reactions give an increase in temperature, and

Crystal characterization

 THERMOGRAVIMETRIC ANALYSIS (TGA)

• It is a method of thermal analysis

in which the mass of a sample is measured over time as the

temperature changes

• TGA can be used for materials

characterization through analysis of characteristic decomposition patterns

• A typical thermogravimetric

analyzer consists of a precision balance with a sample pan

located inside a furnace with a programmable control

temperature.

• The thermogravimetric data

collected from a thermal reaction is compiled into a plot of mass or percentage of initial mass on the y axis versus either temperature or time on the x-axis.

Crystal characterization

 DIFFERENTIAL SCANNING CALORIMETRY (DSC)

• The DSC measures the amount of heat released by a sample as the

temperature is increased or decreased at a controlled uniform state.

• So it can investigate the chemical reaction and measure heats of

Crystal characterization

 SCANNING TUNNELING MICROSCOPY (STM)

• A sharp metal tip is brought suffeciently

close to the surface of the solid sample (0.5-1nm) that their electronwave can overlap and the electron tunnel between the two.

• When a potential is applied to the solid

surface, the electron flow between the tip and the solid to give a tunneling current in the range of pico and nano amperes

• The image usually formed by keeping a

constant tunneling current and measuring the distance thus creating a contours of constant density of state on the surface

Crystal characterization

 ATOMIC FORCE MICROSCOPY (AFM)

• It is based on the detection of very small forces between a sharp tip

and atoms on the surface

• The tip is scanned across the surface at subnanometer distances,

and the deflections due to the attraction or repulsion by the underlying atoms detected

Crystal characterization

 TEMPERATURE PROGRAMMED REDUCTION (TPR)

• It is measuring the reaction of hydrogen with a sample at various temperature • Therefore, it gives the information on the presence of different oxidation state