UNIVERSITI PUTRA MALAYSIA. STRUCTURAL ANALYSIS AND ELECTRICAL CHARACTERISATIONS OF Sr(1-x)CaxTiO3 AND Sr(1-x)BaxTiO3 CERAMICS AZIZAH BINTI ISHAK

Transcription

1 UNIVERSITI PUTRA MALAYSIA STRUCTURAL ANALYSIS AND ELECTRICAL CHARACTERISATIONS OF Sr(1-x)CaxTiO3 AND Sr(1-x)BaxTiO3 CERAMICS AZIZAH BINTI ISHAK FS

2 STRUCTURAL ANALYSIS AND ELECTRICAL CHARACTERISATIONS OF Sr (1-x) Ca x TiO 3 AND Sr (1-x) Ba x TiO 3 CERAMICS By AZIZAH BINTI ISHAK Thesis submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of Requirement for the Degree of Master of Science February 2008

3 DEDICATION This dedication especially goes to my husband Samsudin Bin Mohd Said, my beloved parents Hj Ishak Shamsuddin and Hjh Yusti Isrin; my loving children Hazim, Haziq, Nabilah and Azfar; my brother Aziz, sisters Rozita, Rozana, Hanita and also to my mother-in-law Hjh Indon Shaari and all my dear friends. ii

4 Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science STRUCTURAL ANALYSIS AND ELECTRICAL CHARACTERISATIONS OF Sr (1-x) Ca x TiO 3 AND Sr (1-x) Ba x TiO 3 CERAMICS By AZIZAH BINTI ISHAK February 2008 Chairman : Associate Professor W. Mohamad Daud W. Yusof, PhD. Faculty : Science Ceramic samples of a structural formula Sr 1-x Ca x TiO 3 (SCT) and Sr 1-x Ba x TiO 3 (SBT) were prepared from the starting materials CaCO 3, BaCO 3, SrCO 3 and TiO 2 through the conventional solid state reaction technique. The XRD measurements reveals that the lattice parameter of SrTiO 3 changes after the substitution of Ba 2+ and Ca 2+ while the specimens, Sr 1-x Ba x TiO 3 and Sr 1-x Ba x TiO 3 showed the typical XRD patterns of perovskite polycrystalline structure without a preferred orientation; no second phase was observed. The crystalline structure and dielectric properties of SCT and SBT ceramics with various compositions of x were investigated. The a- and c-axis lattice constants of SCT and SBT were calculated. It is found that the crystal structures of SBT are cubic phase when x 0.6 and tetragonal phase when x 0.7 at room temperature. However, the crystal structures of SCT is orthorhombic when x 0.1 at room temperature. iii

5 The dielectric properties such as real permittivity or dielectric constant (ε ), imaginary permittivity or loss factor (ε ) and dielectric loss (tan δ) have been measured on the sintered disks with respect to frequency in the range 0.01 Hz to 1 GHz at room temperature and varying temperatures from 40 o C to 200 o C. Sample SBT-5 shows the largest value of the real permittivity(ε = 4800), low dielectric loss tangent (tan δ = 2.77) and very low ac conductivity (σ = S/cm) at 0.01 Hz. Ceramic sample SCT shows very low dielectric conductivity,σ. The conductivity increases with frequency over the entire temperature range reflecting higher dielectric loss at higher temperature. In the impedance and modulus relaxation spectroscopy, the magnitude of imaginary impedance, Z maxima decrease with temperature indicating increasing loss in the resistive property of the sample. This behaviour of impedance pattern arises probably due to the presence of space charge in the material. The activation energy decreases from ev to ev when the composition of Ca 2+ is increased from x = 0.3 to x = 0.9. The electric behavior of sample SBT showed that the activation energy has the value of ev and ev. iv

6 Abstrak tesis yang dikemukakan kepada Senat Univesiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains PENGANALISAAN STRUKTUR DAN PENCIRIAN ELEKTRIK BAGI SERAMIK Sr (1-x) Ca x TiO 3 DAN Sr (1-x) Ba x TiO 3 Oleh AZIZAH BINTI ISHAK Februari 2008 Pengerusi Fakulti : Professor Madya W. Mohamad Daud W. Yusof, PhD. : Sains Sampel seramik yang mempunyai formula struktur Sr 1-x Ca x TiO 3 (SCT) and Sr 1- xba x TiO 3 (SBT) telah disediakan daripada bahan-bahan berikut iaitu CaCO 3, BaCO 3, SrCO 3 and TiO 2 menggunakan teknik konvensional tindakbalas keadaan pepejal. Pengukuran XRD menunjukkan parameter kekisi bagi SrTiO 3 berubah setelah didopkan dengan Ba 2+ dan Ca 2+, manakala sampel Sr 1-x Ba x TiO 3 dan Sr 1-x Ba x TiO 3 menunjukkan corak spektrum yang biasa bagi struktur polikristilin perovskit di mana tiada perubahan orientasi; tiada fasa kedua. Struktur kristal dan ciri-ciri dielektrik bagi sample seramik SCT dan SBT dengan komposisi x telah dikaji. Daripada pengiraan pemalar kekisi paksi-a dan paksi-c bagi sample SCT dan SBT, didapati struktur kristal bagi SBT adalah dalam fasa kiub apabila x 0.6 dan fasa tetragonal apabila x 0.7 pada suhu bilik. Manakala struktur kristal bagi SCT adalah ortorombik apabila x 0.1 pada suhu bilik. v

7 Sifat dielektrik seperti permittiviti nyata atau pemalar dielektrik (ε ), permittiviti maya atau faktor kehilangan (ε ) dan kehilangan dielektrik (tan δ) telah diukur ke atas disk yang telah disinter, terhadap frequensi di dalam renj 0.01 Hz ke 1 GHz pada suhu bilik dan juga perubahan suhu dari 40 o C ke 200 o C. Sampel SBT-5 mempunyai nilai nyata pemalar dielektrik yang maksimum (ε = 4800), kehilangan tangent dielektrik yang rendah (tan δ = 2.77) dan nilai minima bagi kekonduksian (σ = S/cm) pada 0.01 Hz. Kekonduksian dielektri, σ, bagi sample seramik SCT menunjukkan nilai kekonduksian yang sangat rendah. Kekonduksian juga bertambah dengan frekuensi disepanjang renj suhu dan ini menunjukkan kehilangan dielektrik yang tinggi pada suhu yang tinggi. Dalam bahagian spektroskopi relaksasi bagi impedans dan modulus, magnitud bagi impedans khayalan Z maksima didapati berkurangan dengan suhu menunjukkan peningkatan dalam kehilangan sifat resistif pada sample tersebut. Perubahan pada corak impedans seperti ini adalah disebabkan oleh kewujudan cas ruang di dalam bahan. Didapati tenaga pengaktifan berkurangan dari ev ke ev apabila komposisi Ca 2+ bertambah dari x = 0.3 ke x = 0.9. Ciri dielektrik bagi sampel SBT-1 menunjukkan tenaga pengaktifan mempunyai nilai ev dan ev. vi

8 ACKNOWLEDGEMENTS Firstly, I am very grateful to ALLAH s.w.t for giving me the strength and patience to complete this research. It is my pleasure to gratefully acknowledge the enthusiastic supervision of my research advisor, Associate Professor Dr. W Mohamad Daud W Yusof for reviewing my thesis and giving insightful comments. His knowledge and depth of commitment to this area of research impressed me greatly and were critical to the completion of this research work. I am also deeply grateful to my co-supervisors, Professor Dr. Abdul Halim Shaari and Professor Dr. W Mahmood for their valuable support and helpful comments throughout my research. I owe special thanks to our XRD lab officer Miss Yusnita Osman, lab assistants, Mr. Razak Harun and Mr. Suhaimi Ibrahim, the technical staff of Electron Microscopy Unit for their kind assistance. I am also indebted to all the lecturers and staff in the Physics Department especially Dr. Halimah Mohamed Kamari whose friendship and knowledge I admire. Finally, I must acknowledge my parents Haji Ishak and Hajjah Yusti for their constant love and support throughout my life. My special thanks to my children M.Hazim, M.Haziq, Aniqah Nabilah and M.Azfar for their love, understanding and time they missed their mother. Also to my mother-in-law Hajjah Indon Shaari for her love and support. During my graduate studies, my beloved husband, Samsudin Bin Mohd Said, has been the source of endless encouragement. Without his support, love and presence, this study could not have been completed. May Allah Bless You All! vii

9 I certify that an Examination Committee has met on 28 February 2008 to conduct the final examination of Azizah Binti Ishak on her Master of Science thesis entitled Structural Analysis And Electrical Characterisations of Sr 1-x Ca x TiO 3 and Sr 1- xba x TiO 3 Ceramics in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations The Committee recommends that the candidate be awarded the degree of Master of Science. Members of the Examination Committee are as follows: Zainal Abidin Bin Sulaiman, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) Sidek Bin Hj Abdul Aziz, PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Internal Examiner) Halimah Binti Mohamed Kamari, PhD Lecturer Faculty of Science Universiti Putra Malaysia (Internal Examiner) Sinin Hamdan, PhD Associate Professor Faculty of Science Universiti Malaysia Sarawak (External Examiner) HASANAH MOHD GHAZALI, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date : 22 July 2008 viii

10 This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirement for the degree of Master of Science. The members of the Supervisory Committee were as follows: W. M. Daud W Yusof. PhD Associate Professor Faculty of Science Universiti Putra Malaysia (Chairman) Abdul Halim Bin Shaari, PhD Professor Faculty of Science Universiti Putra Malaysia (Member) W. Mahmood Mat Yunus, PhD Professor Faculty of Science Universiti Putra Malaysia (Member) AINI IDERIS, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 14 August 2008 ix

11 DECLARATION I hereby declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions. AZIZAH BINTI ISHAK Date : 20 August 2008 x

12 TABLE OF CONTENTS Page DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL SHEETS DECLATION FORM LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS ii iii v vii viii x xiii xiv xvii CHAPTER I INTRODUCTION Electronic Ceramics Scope of Study Objectives of This Research 8 II III IV LITERATURE REVIEW 2.1 Introduction Previous Works on Ferroelectric Ceramics Ferroelectric Materials Strontium Titanate Strontium Barium Titanate System Strontium Calcium Titanate System 22 THEORY 3.1 Introduction Synthesis and Processing Perovskite Structure Principles of Dielectrics Dielectric Behavior Impedance Spectroscopy AC Conductivity Principal types of dielectric functions X-ray Powder Diffraction (XRD) 48 MEHODOLOGY 4.1 Introduction Materials Sample Preparation Structural and Morphological Analysis Dielectric Spectroscopy 61 xi

13 V VI RESULTS AND DISCUSSION 5.1 Introduction Structural Analysis Electrical Properties of SCT and SBT at Room Temperature Sr 1-x Ba x TiO 3 (SBT) System Sr 1-x Ca x TiO 3 (SCT) System Dielectric losses ( tan δ ) AC Conductivity Impedance and Modulus Relaxation Spectroscopy 114 CONCLUSION 6.1 Structural Analysis Dielectrical Analysis Suggestions for Future Research 136 REFERENCES 139 BIODATA OF STUDENT 147 xii

14 LIST OF TABLES Table Page 1.1 Electrical Property constants of different ceramic materials Relation between the impedance and other dielectric functions Capacitance values and their possible interpretation Interplanar spacings d hkl for different crystal systems and their 50 dependency on Miller indices hkl (Connoly, 2007). 4.1 Molecular weight for the starting materials Compounds and weight of substitution (i) Sr 1-x Ca x TiO 3 and 56 (ii) Sr 1-x Ba x TiO Properties of Sr 1-x Ba x TiO 3 system sintered at 1200 o C Properties of Sr 1-x Ca x TiO 3 system sintered at 1350 o C Energy dispersive x-ray parameters for the phase of Sr 0.7 Ca 0.3 TiO Average Grain Size of sample Sr 1-x Ca x TiO Dielectric properties values for sample (a) Sr 1-x Ba x TiO 3 85 (b) Sr 1-x Ca x TiO 3 at room temperature 5.6 Real permittivity values for samples SBT-1 at temperatures ( o C) Values of tan δ for sample SBT-1 at different temperatures 93 and frequencies 5.8 Values of conductivity for sample SBT-1 at different temperatures 95 and frequencies 5.9 Activation energy for various composition in the sample Sr 1-x Ca x TiO xiii

15 LIST OF FIGURES Figure Page 2.1 Classification of crystals according to the symmetry and polarization 15 (Haertling, 1999) 2.2 Variation of dielectric constant with temperature for bulk and thin 19 film barium strontium titanate (Shaw et al., 1999). 3.1 (a) A cubic ABO 3 (BaTiO 3 ) perovskite-type unit cell and (b) three 27 dimensional network of corner sharing octahedral of O 2- ion (Xu, 1991). 3.2 The crystal structure of perovskite barium titanate, (a) above the Curie 29 temperature the unit cell is cubic; (b) below the Curie temperature the unit cell structure is tetragonal with Ba 2+ and Ti 4+ ions displaced to the O 2- ions (Safari et al., 1996). 3.3 The variation of the relative permittivity with temperature for BaTiO3 30 Ceramics with (a) 1 mm grain size and (b) 50 mm grain size (Safari et al., 1996) 3.4 Equivalent circuit of a ferroelectric element (non-resonance operation) 33 (Kingery et al., 2000) 3.5 Schematic representation of different mechanisms of polarization. 38 (Brown et al., 2006) 3.6 Contributions to the frequency-dependent dielectric constant from the 38 Different charge configuration (Brown et al., 2006) 3.7 The real and imaginary components of the complex dielectric 46 susceptibility for the Debye process (Jonscher, 1999). 3.8 A near-debye response showing the characteristic deviation from the 46 Debye shape of χ (ω) (Jonscher, 1999). 3.9 Bragg s Law reflection Flow chart of the synthesis of SBT and SCY by conventional 54 solid-state route. 5.1 XRD diffractogram with indexing of samples Sr 1-x Ba x TiO 3 sintered 66 at 1200 o C. 5.2 Dependence of the lattice parameter and c/a ratio of Sr 1-x Ba x TiO 3 67 sintered at 1200 o C. 5.3 XRD diffractogram of Sr 1-x Ba x TiO 3 system for x = 0.7 sintered at 68 xiv

16 (A) 1250 o C (B) 1350 o C. 5.4 XRD diffractogram with indexing of samples Sr 1-x Ca x TiO 3 sintered 71 at 1350 o C. 5.5 Energy dispersive x-ray images of Sr 0.7 Ca 0.3 TiO Scaaning electron microscope (SEM) images of Sr 1-x Ca x TiO 3 76 as prepared powder at different compositions: (a) x= 0.2 (b) x= 0.3 (c) x= 0.4 (d) x= 0.5 (e) x= 0.6 (f) x= 0.8 (g) x= 0.9 (h) x= Permittivity versus frequency for Sr 0.5 Ca 0.5 TiO 3 and Sr 0.5 Ba 0.5 TiO 3 81 at temperature 40 0 C (a) ε vs frequency (b) ε vs frequency 5.8 Variation of tan δ for Sr 0.5 Ca 0.5 TiO 3 and Sr 0.5 Ba 0.5 TiO 3 samples at 82 room temperature as a function of frequency. 5.9 Variation of ac conductivity for Sr 0.5 Ca 0.5 TiO 3 and Sr 0.5 Ba 0.5 TiO 3 83 Samples at room temperature as a function of frequency Frequency response of permittivity (a) log ε (b) log ε for sample 87 Sr 0.9 Ba 0.1 TiO 3 at different temperature Frequency response of ε, ε for SBT-1 sample Frequency response of tan δ for sample Sr 0.9 Ba 0.1 TiO Frequency response of conductivity for sample Sr 0.9 Ba 0.1 TiO Modulus M relaxation spectroscopy at varying temperatures for sample 98 Sr 0.9 Ba 0.1 TiO 3 (SBT-1) 5.15 Plot of log τ versus 1000/T for sample Sr 0.9 Ba 0.1 TiO 3 (SBT-1) Frequency response of permittivity (a) ε (b) ε for sample SCT-3 at 101 different temperatures Frequency response of permittivity (a) ε (b) ε for sample SCT-4 at 102 different temperatures Frequency response of permittivity (a) ε (b) ε for sample SCT-6 at 103 different temperatures Frequency response of permittivity (a) ε (b) ε for sample SCT-9 at 104 different temperatures Frequency dependence of the dielectric loss tangent as a function of 108 temperature for (a) SCT-3 (b) SCT-4. xv

17 5.20 Frequency dependence of the dielectric loss tangent as a function of 109 temperature for (c) SCT6 (d) SCT Variation of ac conductivity with frequency at different temperatures 112 for (a) SCT-3 (b) SCT Variation of ac conductivity with frequency at different temperatures 113 for (c) SCT-6 (d) SCT Real part of impedance as a function of frequency at different 116 temperatures for (a) SCT-3 (b) SCT Real part of impedance as a function of frequency at different 117 temperatures for (c) SCT-6 (d) SCT Imaginary part of impedance as a function of frequency at different 118 temperatures for (a) SCT-3 (b) SCT Imaginary part of impedance as a function of frequency at different 119 temperatures for (c) SCT-6 (d) SCT Variation of Z and M as a function of frequency measured at varying 121 temperatures from 40 o C to 200 o C for sample SCT Modulus M relaxation spectroscopy at different temperatures for 129 (a) SCT-3 (b) SCT Impedance M relaxtion spectroscopy at different temperatures for 130 (c) SCT-6 (d) SCT Plots of log τ vs 1000/T for sample Sr 1-x Ca x TiO 3 at different 131 Compositions The relationship between activation energy, E against composition, x for 131 sample Sr 1-x Ca x TiO 3. xvi

18 LIST OF ABBREVIATIONS ε Dielectric permittivity ε Real part of permittivity ε Imaginary part of permittivity ε r ε(ω) σ Relative dielectric permittivity Dielectric permittivity as a function of angular frequency Conductivity σ (ω) Conductivity as a function of angular frequency τ ω ω c ω p ac dc Relaxation time (sec) Angular frequency Critical angular frequency Peak angular frequency Alternating current Direct current C* Complex capacitance C Real part of capacitance C Imaginary part of capacitance E G M Activation energy Conductance Modulus M* Complex modulus M Real part of modulus M Imaginary part of modulus xvii

19 MHz Megahertz R Resistance Y* Complex admittance Y Real part of admittance Y Imaginary part of admittance Z* Complex impedance Z Real part of impedance Z Imaginary part of impedance XRD X-ray diffraction SEM Scanning electron microscope EDX Energy dispersive x-ray Sr Ba Ca ST SBT SCT Strontium Barium Calcium Strontium titanate Strontium barium titanate Strontium calcium titanate xviii

20 CHAPTER 1 INTRODUCTION A ceramic has traditionally been defined as "an inorganic, nonmetallic solid that is prepared from powdered materials, is fabricated into products through the application of heat, displays such characteristic properties as hardness, strength, low electrical conductivity and brittleness" (NDT, website). The word ceramic comes from Greek word "keramikos", which means "pottery." They are typically crystalline in nature and are compounds formed between metallic and nonmetallic elements. The atoms in ceramic materials are held together by a chemical bond, The two most common chemical bonds for ceramic materials are covalent and ionic. Covalent and ionic bonds are much stronger than in metallic bonds and, generally speaking, this is why ceramics are brittle and metals are ductile. Many adopt crystalline structures, but some form glasses. The properties of the materials are a result of the bonding and structure. Alkaline earth titanates of general formula ATiO 3 ( A = Ca, Sr, Ba and Pb) and having perovskite structure are useful materials because of their wide applications in the electroceramics industry. Owing to their ferroelectric and piesoelectic properties, BaTiO 3 and PbTiO 3 form the basis of a veriety of electronic devices ( Parkash et. al., 2003). Besides its relevance for electronics, sensor science, electrochemistry and photochemistry, SrTiO 3 (strontium titanate) is an excellent model material for a mixed type conductor because of availability of a detailed knowledge ot its defect 1

21 models, chemical and transport parameters. Strontium tianate (SrTiO 3 ) is an incipient ferroelectric (or quantum paraelectric) in which a ferroelectric phase can be induced at a low temperature by isotrophic substitution or substitutional impurities as well as by external stress (Ping et al., 2008). Perovskite materials with high dielectric permittivity have many applications in dyamic random access memories and ferroelectric non-volatile memories. High-K dielectric materials with low dielectric lossess are rewuired today for various applications in low dimention devices for a large frequency range, including optical domain (Barberacu et. al., 2008). The permittivity control of theses materials by a suitable DC bias field ensures a great opportunity of the phase control of the microwave devices. In this view strontium barium titanate (SBT), bulk ceramics and/or thin films in paraelectric state, is one of the promising material. Solid solution oxides of calcium strontium titante (SCT) with high dielectric constant and dielectric properties of a small temperature coefficient have attracted a great deal of attention for practical use as capacitor dielectrics (Ping et. al., 2008). Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic mixture, dopants and dopant (or defect) distribution ( Irvine et. al.,1990). In the late 1980s, conventional processing methods for producing electroceramic materials (powder compacting, tape casting followed by sintering processes) were increasingly supplemented by thin film deposition techniques. Their properties can be tailored to operation as insulators, ferroelectric materials, highly conductive ceramics, electrodes as well as sensors and actuators. 2

22 1.1 Electronic Ceramics Advanced materials and particularly advanced ceramics play an important role in the future of the world economy. The development and use of advanced ceramics are revolutionizing the field of material science and technology. Advanced ceramics are inorganic, nonmetallic materials with combinations of fine-scale microstructures, purity, complex compositions and crystal structures, and accurately controlled additives. Advanced ceramics can be classified into two groups, structural and electronic ceramics. The study of electronic ceramics involves many disciplines including chemistry, physics, metallurgy, mechanical engineering and material science. Electronic ceramics can be divided into two main groups : (i) (ii) insulators (dielectrics) and semiconductors, and conductors (ionic and mixed). The use of ceramics in electronics is becoming increasingly popular. Insulating ceramics are used extensively in consumer and industrial electronic system. Dielectrics are employed as capacitors to store charge and control the flow of current; for miniaturization of devices the ceramic layers should be as thin as possible. Special low loss dielectrics, operating as resonators are the key to the operation of mobile telephone handsets and base stations. Semiconducting ceramics (non-linear resistors) are employed as protection devices against power surges in almost all electronic and electrical system from computers to power distribution networks. Ceramic superconductors allow the flow of electricity with little or no 3

23 resistance or heat loss. This gives the potential for trains floating on a magnetic cushion of air running at two to three hundred miles per hour and super computers the size of desktop calculators performing calculations thousands of times faster than any computer today. The applications of ceramics in the electronics industry can be divided into two groups: (i) the use of materials for interconnection and packaging of semiconductor circuits, and (ii) the use of ceramics in circuit components which perform a function in their own right, such as capacitors and sensors (Whatmore, 1988). The former application forms a large market and has been well reviewed elsewhere. The latter is particularly interesting because the materials which are used for a wide range of applications are in many cases closely related in crystal structure. In many circuit functions, the material is required to give an electrical response to some stimulus. This can be as simple as giving a large change in induced electrical displacement for a small applied electric field, (i.e. having a large dielectric constant) if the material is for use as a capacitor dielectric. Dielectric science has been a long-standing branch of physics, with close links to chemistry and electrical engineering. Over 130 years ago, Faraday coined the term dielectric to suggest that something analogous to current flow occurs through a capacitor structure during the charging process when current introduced at one plate flows through the insulator to charge the other plate. It is generally accepted that a 4

24 dielectric material interacts with an electric field differently than does free space because the dielectric contain charges that can be displaced. Because all materials contain charges, essentially every material can be classified as a dielectric. Dielectric ceramics can be divided into four categories according to their properties: (i) high permittivity dielectric, ranging between 1000 to 25000, example SrTiO 3 and BaTiO 3. (ii) medium permittivity dielectric, ranging between 50 to 200, example CaTiO 3. (iii) low permittivity dielectric, ranging between 4 to 50, example MgTiO 3. (iv) ultra-low permittivity dielectric, below 3, example SiO 2, and organic polymer (i.e. Teflon AF, parylene). Based on the current technology and the increasing use of portable electronics the need to reduce the capacitance of electronic devices so that higher, less crosstalk and lower power consumption can be achieved using a very low permittivity insulator material. Meanwhile, high permittivity dielectrics have important applications in microelectronics and microwave communication system (Cho et al., 1995). Good ceramic insulators should have relative dielectric constant or relative permittivity ε < 30, electrical resistivity ρ > Ω cm, loss factor, tan δ < 0.001, and consequently dielectric strength > 5 kv mm -1. The review of dielectric properties of some ceramics is presented in Table

25 Table 1.1 : Electrical property constants of different ceramic materials (Herbert, 1985). Material Dielectric constant at 1 MHz Dielectric strength (kv/cm) Air Polystyrene Glass (Pyrex) Alumina Porcelain Titanium dioxide The trend in research of dielectric materials is to develop more low-dielectric constant materials for tomorrow integrated circuitary, The benefit to microelectronic devices are: higher speed, smaller size, higher frequency and lower operational power requirement. 1.2 Scope of Study The ceramics form of Sr 1-x Ca x TiO 3 (SCT) and Sr 1-x Ba x TiO 3 (SBT) are of commercial importance as a ceramic capacitor dielectric and it is of scientific interest since it provides a straightforward example of the effect of solid solution composition of ceramics on dielectric properties. In this study, strontium titanate (ST) powders doped with Ca- and Ba- ions, are conventionally prepared by solidstate synthesis with different compositions and at very high temperatures, 1200 o C to 1350 o C. SCT and SBT powders prepared by this method consist of non-uniform, submicrometer-sized coarse particle. The control of particle size distribution is not 6