UNIVERSITI PUTRA MALAYSIA

PHYSICAL AND ELECTRICAL PROPERTIES OF ZINC-MAGNESIUM-PHOSPHATE GLASSES

NG BENG HONG

FS 2007 49

PHYSICAL AND ELECTRICAL PROPERTIES OF ZINC-MAGNESIUM-PHOSPHATE GLASSES

NG BENG HONG

MASTER OF SCIENCE UNIVERSITI PUTRA MALAYSIA

2007

PHYSICAL AND ELECTRICAL PROPERTIES OF ZINC-MAGNESIUM-PHOSPHATE GLASSES

By

NG BENG HONG

Thesis Submitted to the School of Graduate Studies,

Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science

June 2007

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For my beloved parents, siblings and family

Ng Ching Ai @ Ooi Ah Peng

Lim Chin Lan

Chuah Bee Kuan

Ng Beng Tiong

Ng Beng Wei

Ng Beng Kiat

For showering me with love, understanding and encouragement

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science

PHYSICAL AND ELECTRICAL PROPERTIES OF ZINC-MAGNESIUM-PHOSPHATE GLASSES

By

NG BENG HONG

June 2007

Chairman : Associate Professor Zainal Abidin Talib, PhD Faculty : Science Glasses in a wide range of composition in the ternary system

x(ZnO)-y(MgO)-z(P2O5) where x ranges from 5 to 20 mol %, y ranges from 5 to

20 mol % and z ranges from 50 to 70 mol % have been prepared by traditional

melt quenching technique with ZnO, MgO and P2O5 as the starting raw materials.

X-ray diffraction (XRD), refractive index and electrical properties have been used

to characterize the structural, optical and electrical features. All the sample

glasses at present work have been confirmed to be amorphous by X-ray

diffraction technique using Philips Model 7602 EA Almelo. The refractive indices

of ternary glasses were measured by Ellipsometer and were found to agree with

Lorentz-Lorenz equation where the refractive index increased with the increase of

the density (ρ) and the decrease of the molar volume (Vm) of the glass. The

density of the glass was determined by Archimedes Principle. From the empirical

data, other values such as molar volume and molar refractivity have been

computed. The variations in the molar volume were resulting in variation on the

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density and refractive index of the glasses. From the results obtained, it is obvious

that the refractive index varies with molar refractivity, which depends on the

polarizability of the ions, density and molecular weight in the sample glass. Those

physical properties were found to be sensitively depending on its composition.

Electrical conductivity (σ) was measured in the temperature 30 oC to 300 oC.

Conductivity for the ternary series glasses increased with addition composition of

ZnO or MgO with temperature. Activation energy (Ea) was calculated by the

slope of graph log σ versus 1000/T with Arrhenius equation. The values of

activation energy in the ternary series were recorded in the range of 0.023 eV to

0.112 eV.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains

SIFAK FIZIK DAN ELEKTRIK BAGI KACA ZINK-MAGNESIUM-PHOSPHATE

Oleh

NG BENG HONG

June 2007

Pengerusi : Profesor Madya Zainal Abidin Talib, PhD Falkulti : Sains

Kaca dalam satu julat komposisi diantara system pertigaan

x(ZnO)-y(MgO)-z(P2O5) di mana x dalam julat 5 hingga 20 mol %, y dalam julat

5 hingga 20 mol % dan z dalam julat 50 hingga 70 % telah dihasilkan

menggunakan teknik sepuh lebur dengan ZnO, MgO dan P2O5 sebagai bahan asal

mulaan. Pembelauan sinar-X (XRD), index biasan dan kajian elektrik telah

digunakan untuk menggambarkan ciri struktur, optik dan elektrik yang berlaku

dalam semua sampel. Semua sampel dalam pengajian ini telah disahkan sebagai

amorfus melalui pengukuran pembelauan sinar-X dengan menggunakan mesin

Philips Model 7602 EA Almelo. Indeks biasan pertigaan kaca telah diukur

menggunakan mesin Ellipsometer dan didapati menepati presamaan Lorentz-

Lorenz yang mana nilai indeks biasan tersebut meningkat dengan peningkatan

ketumpatan (ρ) dan penurunan isipadu molar (Vm) bagi sampel kaca. Ketumpatan

kaca telah diukur menggunakan prinsip Archimedes. Dari nilai data empirihal

yang diukur, nilai-nilai lain seperti isipadu molar dan pembiasan molar telah

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dikira. Perubahan isipadu molar mempengaruhi ketumpatan dan indeks biasan

dalam kaca. Hasil kajian jelas menunjukkan bahawa indeks biasan berkadar

songsang dengan pembiasan molar yang bergantung kepada pengutuban ion,

ketumpatan dan berat molekul dalam kaca. Semua sifat fizikal didapati begitu

sensitif pergantungannya kepada komposisi bahan tersebut. Kekonduksian

elektrik (σ) telah diukur dalam julat suhu 30 oC hinggan 300 oC. Kekonduksian

bagi sistem pertigaan kaca didapati meningkat dengan penambahan komposisi

ZnO atau MgO dan peningkatan suhu. Tenaga pengaktifan (Ea) telah dikira

daripada kecerunan graf log σ lawan 1000/T yang mematuhi persamaan Arhenius.

Nilai bagi tenaga pengaktifan dalam sistem pertigaan kaca diperoleh dalam

linkungan 0.023 eV hingga 0.112 eV.

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ACKNOWLEDGEMENTS

I would like to take this opportunity to express my sincere appreciation and

heartfelt thanks to the followings who have contributed in one way or the other

and supported me along the journey towards the completion of this thesis.

First and upmost, I would like to extend my deepest gratitude to the chairman of

the supervisory committee, Associate Professor Dr. Zainal Abidin Talib for

providing me with his invaluable advice and diligent guidance. I am grateful for

the knowledge, sharing of experience, insightful and valuable feedback that he

has imparted on me during the course of the project.

My sincere appreciation is also extended to my two project co-supervisors,

Associate Professor Dr. Wan Daud Wan Yusoff and Professor Dr. Md. Jelas

Haron, for rendering me their extremely useful suggestions, advice,

recommendations and assistance. I would also like to thank them for expending

their time and effort to read and comment on the draft copy of my thesis.

Many thanks to Pn. Halimah, Siti, Emma and Loh for their generous help and

sharing of numerous ideas throughout the progression of this project.

To my beloved parent, brother and family,I would like to extend special thanks

you for their understanding, patient and encouragement. Without them, the path to

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thesis will be a lonely endeavor. Finally, I wish to acknowledge to all my friends

for their help in making this thesis a success.

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This thesis submitted to the Senate of Univrsiti Putra Malaysia has been accepted as fulfillment of the requirement for the Degree of Master of Science. The members of the Supervisor Committee are as follows: Zainal Abidin Talib, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) W. Daud W. Yusoff, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Member) Md. Jelas Haron, PhD Professor Faculty of Science Universiti Putra Malaysia (Member)

Professor/Deputy Dean

School of Graduate Studies Univesiti Putra Malaysia

Date :

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DECLARATION I hereby declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledge. I also declare that is has not been previously or concurrently submitted for any other degree at UPM or other institutions.

NG BENG HONG

Date: 10 September 2007

TABLE OF CONTENTS

Page

DEDICATION i ABSTRACT iii ABSTRAK v ACKNOWLEDGEMENTS vii APPROVAL ix DECLARATION xi LIST OF TABLES xiv LIST OF FIGURES xv LIST OF ABBREVIATIONS/NOTATION/GLOSSARY OF TERMS xvii CHAPTER

1 INTRODUCTION 1.1 Structure and Properties of Rare-Earth Phosphate Glasses 1.2 Motivation 1.6 Aim 1.8 Objective 1.8 Potential 1.9 Chapter Organization 1.9

2 LITERATURE REVIEW 2.1 Review of Binary Glasses, MgO-P2O5 2.1 Review of Density and Refractive Index of Phosphate Glasses 2.5 Review of DC Conductivity of Phosphate Glasses 2.7 Review of the Structural of Phosphate Glasses 2.9

3 THEORY 3.1

Binary Phosphate Glasses (RO-P2O5, R=Alkaline Earth) 3.8 Physical Properties 3.10

3.2.1 Basic Optical – Material Properties 3.10 3.2.2 Electrical Properties 3.12

4 METHODOLOGY 4.1

Chemical Powder Weighing 4.1 Preparation 4.1 Sample Characterization 4.5

4.3.1 Refractive Index 4.5 4.3.2 X-ray Diffraction 4.5 4.3.3 Density 4.5 4.3.4 Molar Volume 4.6 4.3.5 D.C. Conductivity 4.6

5 RESULTS AND DISCUSSION 5.1 Introduction 5.1 Structural Analysis 5.1 Physical Properties 5.4

5.3.1 Density 5.4 5.3.2 Molar Volume,Vm 5.9 5.4 Optical Properties 5.15 5.4.1 Refractive Index 5.15 5.5 DC Conductivity Behavior of the Glasses 5.21 5.5.1 Activation Energy, Ea 5.26

6 CONCLUSION AND SUGGESTIONS 6.1 Conclusion 6.1 Suggestion for further research 6.2

REFERENCES R.1 APPENDICES A.1 BIODATA OF THE AUTHOR V.1

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LIST OF TABLES Table Page 4.1 Nominal compositions for the ZnO-MgO-P2O5 glasses 4.4

synthesized in this study. 5.1 Variation of composition, molecular weight (M.V.), and 5.8 density (ρ) of sample binary and ternary glasses. 5.2 Variation of composition and molar volume (Vm) of binary 5.13 and ternary glasses. 5.3 Average of density and molar volume in ZnO-MgO-P2O5 5.14 Glasses. 5.4 Variation of refractive index, composition of MP series, 5.16 CM series, CP series, and CZ series glasses. 5.5 The comparison the average of refractive index in binary 5.19

and ternary glasses. 5.6 The activation energy, Ea with the composition of mole fraction 5.32

at (ZnO)X-(MgO)0.30-(P2O5)0.70-X glasses (CM series).

5.7 The activation energy, Ea with the composition of mole fraction 5.32

at (ZnO)X-(MgO)0.30-X-(P2O5)0.70 glasses (CP series). 5.8 The activation energy, Ea with the composition of mole fraction 5.32

at (ZnO)0.30-(MgO)X-(P2O5)0.70-X glasses, (CZ series).

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LIST OF FIGURES Figure Page 1.1 Schematic two-dimensional representation of the structure 1.5

of MgO-P2O5 binary phosphate glasses; (a) composed of the basic glass former, P2O5 and (b) showing the effects of Mg cation content on the glass former (taken from Ref. [10]).

2.1 Phosphate tetrahedral sites that can exist in phosphate glasses. 2.10 3.1 Schematic network structure of binary phosphate glasses 3.3

characterizing the depolymerization process with increasing incorporation (top to bottom) of network-modifier cations into the PO4 network (taken from Ref. [27])

4.1 Procedure used to synthesis the binary and ternary phosphate 4.3

glasses systems.

5.1 XRD Spectra of (ZnO)X-(MgO)0.30-(P2O5)0.70-X Glasses 5.2 (CM series). 5.2 XRD Spectra of (ZnO)X-(MgO)0.30-X-(P2O5)0.70 Glasses 5.3

(CP series). 5.3 XRD Spectra of (ZnO)0.30-(MgO)X-(P2O5)0.70-X Glasses 5.3

(CZ series). 5.4 Density of (MgO)X-(P2O5)1-X Glasses (MP series). 5.4 5.5 Density of (ZnO)X-(MgO)0.30-(P2O5)0.70-X Glasses (CM series). 5.5 5.6 Density of (ZnO)X-(MgO)0.30-X-(P2O5)0.70 Glasses (CP series). 5.6 5.7 Density of (ZnO)0.30-(MgO)X-(P2O5)0.70-X Glasses (CZ series). 5.6 5.8 Molar Volume, Vm of (MgO)X-(P2O5)1-X Glasses, (MP series). 5.10 5.9 Molar Volume, Vm of (ZnO)X-(MgO)0.30-(P2O5)0.70-X 5.11

Glasses (CM series). 5.10 Molar Volume, Vm of (ZnO)X-(MgO)0.30-X-(P2O5)0.70 5.11

Glasses (CP series). 5.11 Molar Volume, Vm of (ZnO)0.30-(MgO)X-(P2O5)0.70-X 5.12

Glasses (CZ series).

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5.12 Refractive index of (MgO)X-(P2O5)0.50-X Glasses (MP series). 5.17

5.13 Refractive index of (ZnO)X-(MgO)0.30-(P2O5)0.70-X 5.17 Glasses (CM series).

5.14 Refractive index of (ZnO)X-(MgO)1-X-(P2O5)0.70 5.18 Glasses (CP series).

5.15 Refractive index of (ZnO)0.30-(MgO)X-(P2O5)0.70-X 5.18

Glasses (CZ series). 5.16 Conductivity versus mole fraction for 5.22 (ZnO)X-(MgO)0.30-(P2O5)0.70-X glasses (CM SERIES). 5.17 Conductivity versus mole fraction for 5.22

(ZnO)X-(MgO)0.30-X-(P2O5)0.70 glasses (CP SERIES). 5.18 Conductivity versus mole fraction for 5.24

(ZnO)0.30-(MgO)X-(P2O5)0.70-X glasses (CZ SERIES). 5.19 Log conductivity dependent of temperature for CM Series. 5.28 5.20 Log conductivity dependent of temperature for CP Series. 5.28 5.21 Log conductivity dependent of temperature for CZ Series. 5.29 5.22 The activation energy, Ea as a function mole fraction, x 5.30

CM series system. 5.23 The activation energy, Ea as a function mole fraction, x 5.30

CP series system. 5.24 The activation energy, Ea as a function mole fraction, x 5.31

CZ series system.

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LIST OF ABBREVIATIONS/NOTATION/GLOSSARY OF TERMS

a.c. alternating current

A absorption

A2O alkali oxides

α (ω) absorption coefficient

BO bridging oxygen

C capacitance

CN coordination number

c velocity of light in vacuo (c = 3 x 108 ms-1)

d thickness

d.c. direct current

DBO double bond

e electronic charge

ε’ permittivity or dielectric constant

ε” dielectric loss factor

Ea activation energy

Eg energy gap

Eopt optical band gap

FTIR Fourier transforms infrared

G conductance

I current

IR infrared

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k extinction coefficient

K dielectric constant

M mass of particle

Me metal

MeO metal oxide

NBO non-bridging oxygen

NMR nuclear magnetic resonance

n refractive index

ρ density

Qi number of the BO atoms in a PO4 group

Q charge

R resistor

R reflectance

RO alkaline-earth oxides

Rm molar refractivity

T temperature

Tg transformation temperature (oC)

tan δ loss angle (measure of dielectric losses)

TM transitional metal

TO terminal oxygen

V volume

V voltage

v valency of Me

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Vm molar volume

λ wavelength

ω angular frequency

XRD x-ray diffraction

Z impedance

1.1

CHAPTER 1

INTRODUCTION

Glass is by definition an amorphous substance and an inorganic oxide. In other

words, all glasses are amorphous but not all amorphous solid are necessarily

glasses. Glass can simply be signified as transparent material that is made from

silica with the addition of a few alkali oxides.

Glasses have no underlying regular structure. Glass formed by the process called

“super cooling” processing. A liquid (melt) cool very rapidly below its freezing

point. If the cooling rate is fast enough, the molecules cannot organize themselves

into crystals. Instead, the atoms or molecules making up the glass jumbled

together. They may be packed in tightly until the glass cannot be moved, and are

not packed in a regular way. As the temperature drops, the liquid becomes more

viscous and the molecules more sluggish, thus not giving enough time for the

liquid (melt) to form a regular crystal lattice [1].

Amorphous materials exhibit many properties which are unique to them and are

not shared by crystalline solids. The absence of periodicity, or long-range order,

characteristic of an amorphous solid is most clearly evidenced in a diffraction

experiment, for example using X-rays. Where instead of the sharp Bragg spots or

rings produced by single crystal or polycrystalline samples respectively, broad

1.2

diffuse haloes are observed. The observation of diffuse haloes in a diffraction

experiment is a prerequisite to characterization of an amorphous material.

1.1 Structure and Properties of Rare-Earth Phosphate Glasses

In this study, magnesium-phosphate (M-P) glasses are chosen as the base glass.

The appearance of the base glass is colourless and transparent. The phosphate ion

is a polyatomic anion. It consists of one central phosphorus atom surrounded by

four identical oxygen atoms in a tetrahedral arrangement with the empirical

formula PO43- [2]. The structure of vitreous P2O5 is thought to consist of a

3-dimensional network of corner-sharing PO4 tetrahedral each of which is

decorated with a non-bridging P=O bond.

As alkali and transition metals (network-modifying elements) is added to form a

binary or ternary of phosphate glass, a structural transformation from a 3-D

network of P2O5 to a complex chain structure takes place through the generation

of additional non-bridging oxygen. However, the chemical durability of glasses

was improved with the addition of mixed oxide [3].

To their chemical durability, the phosphate glasses can be melted at lower

temperatures (1000oC to 1200oC) than many silicate glasses. Phosphate glasses

are fluid and easily poured, do not easily devitrified, and can contain large

amounts of alkali and alkaline earth oxides without any serious reduction in their

1.3

chemical durability [4]. Based on the properties, these glasses are excellent

materials for use in the vitrification and safe disposal of nuclear and other

hazardous wastes [5]. Therefore, understanding the correlation between the

structure modification induced by various metal-oxide additives and the physical

and chemical properties represents one of the most important aspects of materials

research on phosphate glass.

Alkali, alkaline-earth and many of others metal oxides form glasses when melted

with P2O5 materials. Phosphate glasses are of technological interest due to their

several unique properties, such as high thermal expansion coefficient, low glass

transition temperature and low softening temperature would make them

characterized by good infrared (IR) transmissions [5, 6, 7]. Due to their physical

properties, the phosphate glass have several advantages that more conventional

than silicate glass [8].

Alkaline-earth phosphate glasses are important for technological applications in

various fields of optics. These glasses are structurally interesting because they

accept a wide range of alkaline-earth. Properties of a glass are governed by its

structure which in turn depends on its chemical composition.

It is well known that several transition metal oxides viz. V2O5, ZnO, MgO, etc.

when heated with a glass former like P2O5, B2O3, etc. form binary or ternary

glasses on quenching the melt. The MgO-P2O5 glasses have been studied

1.4

extensively by several authors [9, 10]. The pure MgO-P2O5 glasses are, in general,

very unstable (hygroscopic) and their conductivity is also low. Both the

conductivity and the stability of these glasses are found to increase by the small

addition of various oxides of alkaline earth.

Magnesium phosphate glasses are classified into so-called “anomalous

phosphate” since MgO-P2O5 glasses has anomalies in many of its physical

properties [9]. The properties of the magnesium phosphate glasses are strongly

influenced by the strengthening effect of Mg2+ and the characteristic of binary

phosphate glasses depended on the availability of terminal oxygen (TO) to

coordination to the cations in phosphate system.

In 1995, Higazy [10] measured the electrical conductivity and electrical constant

of MgO-P2O5 glasses. He stated that Mg appear to belong to the category of ions

which can occupy interstitial positions in glasses as cations forming, Mg2+. In

glasses, cations forming strongly ionic conduction and therefore directional bonds

with oxygen are described as part of the glass network. So consider for the studied

glass system the Mg ions enter the glass network interstitially (see Fig. 1.1).

Hence, some network bonds (P-O-P) are broken and replaced by ionic force

between Mg ion and singly bonded oxygen atoms.

1.5

Fig.1.1. Schematic two-dimensional representation of the structure of

MgO-P2O5 binary phosphate glasses; (a) composed of the basic glass former,

P2O5 and (b) showing the effects of Mg cation content on the glass former

(taken from Ref. [10]).