73  

CHAPTER - 3

EXPERIMENTAL TECHNIQUES AND INSTRUMENTS

This chapter gives a brief description about the basic experimental techniques/

instruments used / employed in the present investigation. Details of experimental

procedure are separately discussed in the relevant chapters. The basic techniques used

are: X-ray diffraction for ascertaining the amorphous nature of synthesized samples,

Differential Scanning calorimeter for determining the glass transition temperature,

Vickers Hardness Tester for determining the mechanical properties, Impedance

analyzer for ac / dc measurements, MAS NMR Spectrometer for understanding the

structure and dynamics of nucleus, FTIR Spectrometer for obtaining structural

information of glasses, Raman Spectrometer for studying the rotational, vibrational and

other low frequency modes in a system, ESR Spectrometer for studying the

paramagnetic centers of the sample, Photoluminescence Spectrometer and UV

absorption Spectrometer for studying the nature of glasses and hence find its potential

applications.

3.1 Test Samples

The general formulae and compositions of the samples used for the synthesis are listed

below:

Sample Chemicals used Composition

 

Na2O- B2O3–V2O5

Sodium carbonate (Na2CO3)

Orthoboric acid (H3BO3),

Vanadium pentoxide (V2O5)

[(100 – x)0.5( Na2O – B2O3 )

– x V2O5] (where x = 10, 15,

20, 25, 30, 35, 40, 45, 50 mol

%)

74  

NaPO3–ZnO –MnO2

Sodium Hydrogen Phosphate

(NaHPO4)

Zinc oxide (ZnO)

Manganese oxide (MnO2)

[(80– x) NaPO3 – 20 ZnO –

x MnO2] (where x = 1, 3, 5,

7.5, 10 mol %)

NaPO3 –ZnO –Nd2O3

Sodium Hydrogen Phosphate

(NaHPO4)

Zinc oxide (ZnO)

Neodymium oxide (Nd2O3)

[(80 – x) NaPO3 – 20 ZnO –

x Nd2O3] (where x = 0, 0.1,

0.3, 0.5, 0.7 mol%)

3.2 X-Ray Diffraction

Powder X-ray diffraction (XRD) method is used to measure the diffraction of

X-rays from the plane of atoms within the material to investigate and quantify the nature

of materials. Diffraction occurs when X-rays having wavelength of the order of a few

angstroms interact with a structure whose repeat distance is about the same as the

wavelength of X-rays. Depending upon the atomic arrangement, the reinforcement

between the reflected rays occurs based on the selective Bragg’s law condition 2d sin θ

= n λ, where ‘d’ is the inter-planar spacing of the specimen, ‘’ the glancing angle, ‘n’

the order of the reflection and ‘λ’ the wavelength of the X-rays used.

XRD pattern is a non-destructive testing method for the identification of

crystalline and amorphous phases. The main components of the system are the

monochromatic X-ray source, finely powdered sample which is rotated against the

center (goniometer) and data collector such as film, strip chart or detector systems.

Fig.3.1 represents the schematic representation of X-ray diffractometer.

75  

Fig. 3.1. Schematic representation of X-ray diffractometer

The X-rays after undergoing diffraction from the sample gets concentrated on

the detection slit, which are detected by scintillation detectors and are converted into

electrical signals. The pulse height analyzer picks up these signals after eliminating its

noise components. Spectra is recorded with the help of a chart recorder which runs

synchronous with the goniometer. The plot of angular positions and intensities of the

resultant diffraction peaks produces a pattern which is characteristic of the sample. The

glassy or amorphous materials do not have a long-range atomic order, therefore, a

diffraction pattern containing sharp peaks are not observed as in the case of crystalline

materials. The nature of the glasses, whether it is amorphous or crystalline, have been

determined with the help of X-ray diffraction (XRD) using Rigaku Model DMAX-TC

(SSCU, IISc, Bangalore). The photograph of the instrument used for the analysis is

shown in Fig.3.2.

76  

 

Fig. 3.2. A photograph of X-ray diffractometer (XRD) used in the experimental

analysis.

3.3 Modulated Differential Scanning Calorimeter (DSC)

Calorimetry is an efficient technique, normally used for the study of the

thermodynamic properties of materials like phase transformation, specific heat, glass

transition temperature, heat capacity etc. A schematic diagram of DSC is shown in

Fig.3.3.

Fig. 3.3. Schematic diagram of Differential Scanning Calorimeter (DSC).

77  

It can measure enthalpy changes in samples because the changes in their

physical and chemical properties are dependent on time or temperature. In this

technique, the difference between the temperature and heat flow of a sample and a

reference material are studied by subjecting them to temperature variation in a

controlled atmosphere. There is a constant temperature difference ‘ΔT’ between the

sample and reference material, since they have different heat capacities. This difference

in temperature (ΔT), between sample temperature (Ts ) and reference temperature (Tr)

is detected during heating/cooling and plotted against sample temperature ‘Ts’ and is

known as baseline. Glass transition (Tg) is manifested by a drastic change in the base

line, indicating a change in the heat capacity of the sample under consideration. If the

sample undergoes a physical change or a chemical reaction, its temperature will change

while the temperature of the reference material remains the same. That is because

physical changes in a material such as phase changes and chemical reactions usually

involve changes in enthalpy, the heat content of the material. In the sample, endotherms

or exotherms are obtained during phase transformation depending on the energy

absorbed or released. DSC has been widely used to find the glass transformation

temperature (Tg), changes in heat capacity, etc.

Glass transition temperature (Tg) and heat capacity (Cp) of the investigated

glasses were recorded using a Differential Scanning Calorimeter using METTLER-

TOLEDO DSC-1 (SID, IISc, Bangalore) at a heating rate of 2 degree per minute. Glass

transition temperature (Tg) were determined using the intersection of the extended

linear region in the thermograms. The photograph of the instrument used for the

analysis is shown in Fig. 3.4. High temperature furnace together with a sample carrier

suitable for Cp measurements and blank aluminium crucibles were used as reference

samples. All the recordings were carried out in nitrogen atmosphere to prevent samples

78  

from oxidation. The glass transition temperature and other glass forming ability

parameters are evaluated to an accuracy of ± 1o C.

Fig 3.4. A photograph of Differential Scanning Calorimeter (DSC) used in

the experimental analysis.

3.4 Fourier Transform Infrared (FTIR) Spectrometer

Infrared (IR) spectroscopy is one of the most powerful analysis techniques

which offers the intensity measurements for the quantitative analysis. This technique

is based on the fact that the specimen under study shows marked selective absorption

in the infrared region. After absorption of the IR radiation, the molecules of the

specimen vibrate and give rise to close-packed absorption bands, called an IR

absorption spectrum which may extend over a wide wavelength range. If the natural

frequency of vibration of some part of the molecule is the same as the frequency of the

incident radiation then a molecule will absorb IR radiation [Griffiths 1983]. When

exposed to infrared radiation there occurs a change in the dipole moment of the

molecules due to selective absorption of radiation of specific wavelengths by the

molecules in the test sample. Thus, the vibrational energy levels of these molecules

shift from ground to excited state. The energy gap of the vibration is used to determine

79  

the frequency of the absorption peak and the number of absorption peaks can be

determined by the number of vibrational freedom of the molecule. The intensity of

absorption peaks can be correlated to the change of dipole moment and the feasibility

of the energy level transition. Various bands in the IR spectrum will correspond to the

characteristic functional groups present in a chemical substance. Therefore, one can

readily obtain adequate information on the structure of the molecule by analyzing the

infrared spectrum. The IR spectrum of a chemical specimen is a finger print for its

identification. The absorption radiation of most organic compounds and inorganic ions

is found to be in the most common region of infrared absorption spectroscopy as its

radiation is found to be in the range of 4000 ~ 400 cm-1. One of the simplest types of

interaction of an external electromagnetic field with solids is the absorption of infrared

light. The frequency of IR radiation lies in the range 30 cm-1 ≤ 0 ≤ 2000 cm-1 and thus

coincides with typical frequencies of atomic vibrations. In glasses, the atomic vibrations

in the IR domain are quite similar to those in crystalline materials.

FTIR Spectrometer consists of a source, interferometer, sample holder, detector,

amplifier, convertor and an analyzer. The radiation generated from the source asses

through the interferometer to the sample and reaches the detector. Then the amplifier

amplifies the signal using an amplifier. This amplified signal is converted to digital

signal by an analog-to-digital converter. Finally, the Fourier transform is carried out by

transferring the signal to a computer [Perkins 1986]. The basic components of an FTIR

spectrometer are shown schematically in Fig.3.5.

80  

Fig. 3.5. Schematic illustration of an FTIR system [Perkins 1986]

In the present investigation, FTIR Spectrometer (Thermo-Nicolet 6700 Range: 400 to

4000 cm-1 at SID, IISc, Bangalore) was used to carry out measurements in the range of

400-4000 cm-1 using a KBr beam splitter and a deuterated L-alanine doped triglycine

sulfate (DLaTGS) detector with a KBr window. The photograph of the instrument used

for the analysis is shown in Fig.3.6.

Fig. 3.6. A photograph of FTIR Spectrometer used in the experimental analysis.

81  

3.5 Raman Spectrometer

Raman Spectrometer usually consists of source, sample holder, monochromator

and a detector. The sample is illuminated with a monochromatic light and the scattered

light is observed at right angles to the incident radiation. Light from the helium-neon

laser beam enters the sample compartment horizontally. Then the scattered light from

the sample cell is focused on the entrance slit of the monochromator. If depolarization

measurements are to be made, the Raman emission is first allowed to pass through an

analyzer prism before entering a monochromator which is a double –pass grating. A

double-pass grating acts as a filter which keeps stray light from the unshifted laser

wavelength to a minimum. The spectrum is further focused onto a Photomultiplier tube.

This detector is connected to an amplifier and a recorder which directly provides the

Raman spectrum. A block diagram of Raman spectrometer [Chatwal Anand 1979] is

shown in Fig.3.7.

 

Fig. 3.7. Block Diagram of Raman Spectrometer

82  

In the present investigation, Lab RAM HR (UV) system (HORIBA Jobin Yvon

CCNSE-CHL-OPTCL-LRHR-E01 at CNSE, IISc, Bangalore) was used which is fully

automated with fast 2D and 3D imaging capability with a wide range of detectors and

visualization options. This system allows the collection of large area Raman images,

using the X, Y and Z mapping features in few seconds / minutes with the help of 325

nm and 514 nm LASER using CCD detector. The measurements were carried out in

the range of 200-1500 cm-1 making use of an excitation wavelength of 514.5 nm from

a 1mW laser at room temperature. The photograph of the instrument used for the

analysis is shown in Fig. 3.8.

Fig. 3.8. A photograph of Raman Spectrometer used in the experimental

                                  analysis.

 

 

83  

 

 

3.6 Nuclear Magnetic Resonance (NMR) Spectrometer

NMR is a phenomenon found in magnetic system that possess both magnetic

moments and angular momentum. The magnetic energy levels are created by keeping

the nuclei in a magnetic field. Without the magnetic field the spin states of nuclei are

degenerate and energy level transition is not possible. But as soon as the magnetic field

is applied, the separate levels and radio frequency radiation can cause transition

between these energy levels. The excitation of nuclear spin states occurs due to the

absorption in the low-energy radio-frequency part of the spectrum. Certain nuclei like

1H, 13C, 19F and 31P are tuned to NMR spectrometers. This high-resolution spectroscopy

can distinguish and count the atoms in different locations of the molecules of certain

nuclei. NMR is a powerful tool for investigating nuclear structure and is used for

understanding mainly the structure and dynamics of molecules in the matter. Fig.3.9

represents the block diagram of computer based NMR spectrometer [Constantin Job et

al 1994].

Fig. 3.9. Overall block diagram of computer based NMR Spectrometer

84  

The Receiver, Preamplifier and Amplifier comprises the basic spectrometer. RF

amplifier, Receiver and Preamplifier are enclosed in an external aluminum enclosure

to minimize the electrical noise and interference with outside sources and to reduce

temperature effects. Virtually all the components of a standard NMR spectrometer

console are enclosed within the personal computer and are directly connected to the

microcomputer.

3.7 MAS NMR Spectrometer

MAS NMR spectra of finely powdered glass samples were recorded on

BRUKER DSX-300 NMR Spectrometer (NMR Lab, IISc, Bangalore) operating at

96.28 MHz. Sample spinning speeds were generally 7 kHz / minute. The chemical shift

values were referenced against saturated trimethyl boron and neat VOCl3 liquid by

using saturated NaVO3 aqueous solution (-578 ppm) for the 11B and 51V spectra,

respectively.

The measurements were made at room temperature (298K). The magnetic field

is of the range 7.04 Tesla. This spectrometer can be extensively used for Magic Angle

spinning studies and has multinuclear facilities and covers all the nuclei resonating

between 44 - 121 MHz. For Magic Angle Spinning, it has a capacity to function at a

temperature range of 300 -363 K. The achievable spinning speed is 10 - 12 KHz. The

spinning angle can vary from 0 - 90 degrees for angle dependent studies in spinning

experiments. NMR of boron and vanadium samples were studied with this instrumental

set up. The photograph of the instrument used for the analysis is shown in Fig. 3.10.

85  

Fig. 3.10. A BRUKER DSX-300 NMR Spectrometer used in the

                           experimental analysis. 

3.8 Electron Paramagnetic Resonance (EPR) Spectrometer

EPR is another important and powerful technique to study paramagnetic

centers (transition metal ions having free radicals, partially filled inner electron shells

etc). It involves magnetic dipole interactions between Zeeman levels produced by the

removal of spin degeneracy by an applied magnetic field. These transitions are induced

when an appropriate electromagnetic field at right angles is applied to the direction of

observation [Ayscough 1967]. The EPR spectrum like NMR, results from transition

from one spin state to the other state of an electron. Each spin state has an energy level,

the transition in EPR is induced by the radiation of microwave frequency rather than by

86  

radio frequency. The main parts of an EPR spectrometer consists of source, sample

cavity, microwave bridge, magnets, detectors, oscilloscope and pen recorder. Fig.3.12

shows the block diagram of EPR spectrometer. The radiation source is usually a

Klystron, which is a stable high power microwave source. The sample is stationed in a

resonant cavity which passes microwaves through an iris. The weak signals from the

sample are amplified with the help of cavity located in the middle of an electromagnet.

Around 100 mg powder of the sample is placed in a sample cavity and is subjected to

microwave magnetic field of constant frequency which is perpendicular to magnetic

field ‘H’. H is varied by the electromagnetic excitation current and when the resonance

condition is fulfilled, a part of the microwave energy will be absorbed by the sample.

When H is varied, the detector output at each point on the absorption signal forms a

sinusoidal wave which is amplified by a selective amplifier. In practice, the microwave

bridge control contains most of the external components, such as the source and

detector. Additionally, other components like attenuator, field modulator and amplifier

are also included to enhance the performance of the instrument. The EPR spectra is

recorded either by first differential curve or second differential curve of the absorbed

signal.

In the present work, Bruker EMX spectrometer operating at X-band (9.025

GHz) microwave frequency was used. EPR of magnesium and vanadium samples were

studied using the spectrometer shown in Fig.3.11 [www.pharmatutor.org].

87  

Fig. 3.11. Block diagram of ESR spectrometer showing essential components.  

3.9 Ultraviolet - Visible (UV) absorption Spectrometer

The Ultraviolet and Visible spectroscopy is a valid and precise analytical

laboratory experimental technique that allows the analysis of a substance. Specifically,

the absorption, transmission and emission of ultraviolet and visible light by matter is

measured by the ultraviolet and visible spectroscopy. The wide ranging electromagnetic

radiation spectrum consists of only a small portion of the Ultraviolet and visible light.

In the practical sense, spectroscopy measures the absorption, emission or scattering of

electromagnetic radiations by atoms or molecules. In the present study we are

calculating the band gap and the related optical parameters of glass samples.

Instruments for measuring the absorption of UV or visible radiation comprises of

88  

source, monochromatic, sample holders (reference cell and sample cell), detector,

signal processor and chart recorder. Fig. 3.12 [www. chemguide. co. uk] shows the

schematic representation of components and working of UV absorption Spectrometer.

Fig. 3.12. Block diagram of UV absorption Spectrometer showing essential

components.

When a light source consisting of the entire visible spectrum plus the near ultra-

violet is made to fall on a rotating diffraction grating, it allows light from the whole

spectrum (a tiny part of the range at a time) into the rest of the instrument. The light

coming from the diffraction grating and slit will strike the rotating disc and gets

reflected alternately through the reference cell. The sample cell contains a solution of

the substance and the solvent is chosen so that it doesn't absorb any notable amount of

light in the wavelength range (200 - 800 nm). Chart recorders usually plot absorbance

against wavelength.

In the present work Perkin - Elmer (Lambda-35) spectrometer [CNSE, IISc,

Bangalore], which is a double beam spectrophotometer with variable band width from

0.5 - 4 nm was used. It provides sensitive measurements with accessories such as fiber-

89  

optics probes and integrating spheres for solid samples for online and macro sample

testing with advanced color software. Its wavelength ranges from 190-1100 nm and has

a variable bandwidth for higher resolution. It possess 50 mm integrating sphere for

reflectance measurements and thus measures absorbance of liquid, thin films and

powder samples. Fig. 3.13 shows the experimental setup used for the optical absorption

measurements in the present investigation.

Fig. 3.13. Perkin- Elmer (Lambda-35) spectrometer

3.10 Photoluminescence (PL) Spectrometer

Photoluminescence (PL) occurs under optical excitation with the emission of

light from the sample under consideration. When light of sufficient energy is incident

on the sample, photons are absorbed and electronic excitations takes place. Finally, if

this relaxation is radiative, the electrons return to the ground state and the emitted light

will be photoluminescence signal. From the intensity of the PL signal, the measure of

the relative rates of radiative and non-radiative recombinations can be obtained.

Because PL depends much on the nature of the optical excitation, the excitation energy

usually selects the initial photo-excited state and governs the depth of the penetration

90  

of incident light. Rare-earth–doped glasses can be usefully investigated by using PL

techniques. The experimental set up of PL is as shown in Fig. 3.14.

Fig. 3.14. Diagram of PL experiment set-up

Photoluminescence occurs when a laser source adjusted to a wavelength close

to the band gap energy of the sample is lead onto the sample. Light will be emitted from

the sample at wavelengths based on the composition of the sample. The sample is

aligned such that the reflected laser beam and the PL emission transmit in different

directions. The emitted light is targeted into a fiber optic cable and then to a

spectrometer. Filter placed in front of the fiber input will remove the stray incident

laser light. Wavelengths are diffracted in different directions with the help of

diffraction grating inside the spectrometer towards an array of photo-detectors, which

measures the intensity of each component of wavelength. The computer finally displays

a PL spectrum by interpreting the digital information. The relative intensities of light

of different wavelengths entering the detector is an indicator of the spectrum [Gfroerer

2000].

91  

In the present investigation, Lab RAM HR (UV) system (HORIBA Jobin Yvon

CCNSE-CHL-OPTCL-LRHR-E01 at CNSE, IISc, Bangalore) was also used for PL

measurements. The measurements were carried out in the range of 200-1500 nm using

an excitation laser source at 325 and 514.5 nm (depending upon the sample). The

photograph of the instrument used for the analysis is shown in Fig. 3.8.

3.11 Electrical conductivity measurements

Electrical properties of glasses are some of the most important aspects to be

studied for their applications in electrical and electronic industries. A substance is said

to be electrically conducting when free electrons or ions within make the flow of current

possible. This property is characterized by the parameter called electrical conductivity,

which is reciprocal of resistivity. Electrical conductivity measurements [Veeranna

Gowda et al 2013] were carried out as a function of frequency and temperature by

employing a Hewlett- Packard (HP 4192A) impedance gain phase analyzer of

frequency range 10Hz -10MHz and the temperature range of 303 K - 343 K. A home

built cell assembly (having two terminal capacitor configuration and spring loaded

silver electrodes) was used for the measurements. The bulk electrical resistivity is

determined by the complex impedance analysis of the frequency- dependent

capacitance and conductance data. A schematic diagram of the fabricated conductivity

cell is shown in Fig. 3.15.

92  

Fig. 3.15. Schematic representation of the cell used for conductivity

measurements [Veeranna Gowda et al 2013].

The sample temperature was measured using a Pt–Rh thermocouple positioned very

close to the sample. The temperature was controlled using a Heatcon (Bangalore, India)

temperature controller. Annealed glass pieces were coated with silver paint on both

sides so as to serve as electrodes for measurements. The capacitance (C) and

conductance (G) of all the samples were measured from the impedance analyser. These

were used to evaluate real and imaginary parts of the complex impedance using

standard relations (Macdonald 1983; Sundeep Kumar and Rao 2004).

The conductivity is calculated using the values of bulk resistance (Rb), radius

(r) and thickness (t) of the glass pieces using the equation   . The d.c

conductance’s were determined from the semicircular complex impedance plots. Thus,

the conductivity ‘σ’, activation energy ‘Ea’, dielectric permittivity ‘ ε ' and electric

modulus M* can be calculated from the real and imaginary parts of the impedance data.