G8176 PREPARATION, CHARACTERISATION AND MICROWAVE DIELECTRIC PROPERTIES OF A,B,.,O], (o=S, 6, 81 TYPE PEROVSKITE COMPOUNDS THESIS SUBMITTED TO COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY IN FULFILMENT OF REQUIREMENT FOR THE DEGREEOF DOCTOR OF PHILOSOPHY IN PHYSICS I. N. JAWAHAR Undertheguidanceandsupervisions of Dr.M.T. Sebastian (Supervisor) Dr. P. Mohanan (Co-Supervisor) REGIONAL RESEARCH LABORATORY (CSIR) THIRlNANANTHAPURAM AUGUST 2002 Fax: + + 91- (0) 471 - 491712 Phone: 471- 515294 (OJ.471- 446901 (R) Email: [email protected]@eth.net ~ Council of Scientific & Industrial Research ~.. "." REGIONAL RESEARCH LABORATORY THIRUVANANTHAPURAM - 695 019. INDIA Dr. M. T. SEBASTIAN Scientist CERTIFICATE This is to certify that this thesis entitled "PREPARATION, CHARACTERISATION AND MICROWAVE DIELECTRIC PROPERTIES OF AnBn-103n (0=5, 6, 8) TYPE PEROVSKITE COMPOUNDS", is an authentic record ofthe investigation carried out by Mr. I. N. JAWAHAR at Regional Research Laboratory (CSIR), Thiruvananthapuram, India under my supervision and guidance. This thesis orany partthereofhas not been submitted for any other degree. Thiruvananthapuram Supervisor 9} /62 Dated: o&, CERTIFICATE This is to certify that this thesis entitled "PREPARATION, CHARACTERISATION AND MICROWAVE DIELECTRIC PROPERTIES OF AnBn-103n (n = 5, 6, 8) TYPE PEROVSKITE COMPOUNDS", is an authentic record ofthe investigation carried out by Mr. I. N. JAWAHAR at Regional Research Laboratory (CSIR), Thiruvananthapuram, India under my supervision and guidance. This thesis orany part thereofhas not been submitted for any other degree. Dr. P. Mohanan Co- Supervisor Professor Kochi Department ofElectronics l~\o~."1.-- Dated Cochin University ofScience and Technology CONTENTS Preface Acknowledgements v ChapterI INTRODUCTION 1.1 Dielectric resonators 1 1.1.1 Resonance 3 1.1.2 Typesofdielectric resonators 5 \.\.3 Analyticaldetermination offrequencies 6 1.1.4 Modechart 8 1.2 Materials Requirements 12 1.2.1 Highdielectric constant 12 1.2.2 Highquality factor (lowdielectric loss) 13 \.2.3 Thecoefficientoftemperature variation ofthe resonantfrequency("ef) 15 1.3 Polarisation mechanisms in dielectrics 16 lA Behaviour ofdielectric with respect to frequency 17 1.4.\ Resonantabsorption 18 1.4.2 Relaxation absorption 21 1.5 Dielectric constant 22 1.5.\ Determination ofEr 24 1.6 Quality factor (Q factor) 24 1.6.1 Determination ofQfactor 26 1.7 Temperature coefficient ofresonant frequency 27 1.7.\ Determinationof"ef 28 1.8 Dielectric resonators at microwave frequencies 29 1.9 Dielectric resonator materials 30 1.10 Applications ofdielectric resonators 30 1.10.1 Dielectric resonatoroscillators (DRO) 31 1.10.2 Di1ectricresonatorfilters 32 1.10.3 Whispering Gallery Mode (WGM) DRs 33 1.10.4 Dielectricresonatorantennas(DRAs) 33 References 34 Chapter 2 PREPARATION AND CHARACTERISATION 2.1 Ceramic preparation 40 2.1.1 Powderforming 41 2.1.1.1 Weighingofraw materials 41 2.1.1.2 Mixing 42 2.1.1.2.1 Ball milling 43 2.1.1.3 Calcination 45 2.1.1.4 Grinding 46 2.1.1.5 Shapingor forming 47 2.1.2 Sintering 49 2.1.2.1 Sinteringaids 51 2.1.3 Specificpreparation methods 51 2.2 Microwave characterisation ofdielectric resonators 53 2.2.1 Introduction 53 2.2.2 Material characterisation at microwave frequencies 55 2.2.2.1 MeasurementofEr 57 2.2.2.2 Measurement ofquality factor (Q) 65 2.2.2.3 Measurement ofr, 68 2.3 Othercharacterisation ofDRceramics 69 2.3.1 PowderX-ray Diffraction (XRD) 69 2.3.2 ScanningElectron Microscopy (SEM) 70 2.3.3 Spectroscopic methods 70 References 71 Chapter 3 THEAsB (A=Ba, Sr, Mg, Ca, Zn; B=Nb, Ta) 401S MICROWAVE DIELECTRIC CERAMICS 3.1 Introduction 76 3.2 TheAsB401S(A=Ba, Sr, Mg, Ca, Zn; B=Nb, Ta) ceramics 78 3.2.1 Preparation and characterisation 78 3.2.2 Results and discussion 81 3.2.2.1 Densityand X-ray diffraction 81 3.2.2.2 Microwave dielectric properties 88 3.3 FarInfrared and submillimeterstudies ofAsB401S (A=Ba, Sr, Mg, Ca, Zn; B=Nb, Ta) ceramics 91 3.3.1 Introduction 91 3.3.2 Experimental 94 3.3.3 Results and Discussion 95 3.3.3.1 Infraredand submillimeterspectra 95 3.3.3.2 Phonon spectraand crystal structure 100 3.3.4 Conclusion 105 3.4 Bas-xSrxTa401S,BasNbxTa4-xOlSand SrsNbxTa4-xOlS solid solution phases 107 3.4.1 Introduction 107 3.4.2 Experimental 108 3.4.3 Results and discussion 109 3.4.3.1 Density 109 3.4.3.2 X-ray diffraction analysis III 3.4.3.3 Microwave dielectric properties 119 3.4.3.3.1 Bas-xSrxT'40Is 119 3.4.3.3.2 BasNbxT'4-xOIS 121 3.4.3.3.3 SrsNbxTa4-xO\S 122 3.4.4 Conclusion 125 3.5 The microwave dielectric properties of(1-x)ZnNb206- xZn3Nb20S mixtures 126 3.5.1 Introduction 126 3.5.2 Experimental 127 3.5.3 Results and discussion 128 3.5.3.1 Density 128 3.5.3.2 X-ray diffractionanalysis 131 3.5.3.3 Microwave dielectric properties 133 3.5.4 Conclusion 138 3.6 The microwavedielectric properties of xZnO-(5-x)MgO-2Nb2OS 138 3.6.1 Introduction 138 3.6.2 Experimental 139 3.6.3 Results and discussion 140 3.6.3.1 Densityand XRD 140 3.6.3.2 Microwave dielectric properties 144 3.7 Conclusion 146 References 148 Chapter 4 THEMICROWAVE DIELECTRIC PROFERTIES OFMO-La20rTi02 (M=Ca, Sr, Ba) CERAMICS 4.1 Introduction 151 4.2 Preparation and characterisation 153 4.3 Results and discussion 155 4.3.1 X-ray diffraction and SEM analysis 156 4.3.2 Microwave dielectric properties 161 .. 4.4 Conclusion 166 References 167 Chapter 5 ANOVEL METHOD OF TEMPERATURE COMPENSATION BY STACKING POSITIVE AND NEGATIVE RESONATORS 'rf 5.1 Introduction 169 5.2 Experimental 172 5.3 Results and Discussion 174 5.3.1 BasNb401S: 5ZnO-2Nb20sstacked resonators 174 5.3.2 BasNb40IS: Sr(YlI2NbIn)03 stackedresonators 180 5.4 Conclusion 183 References 185 Chapter 6 SUMMARYAND CONCLUSION 187 PREFACE Dielectric Resonators (DR) are ceramic pieces'that can act as frequency determining components at microwave frequencies. DRs should have high dielectric constant (er) in the range 20 to 100 for better miniaturization, high Qfactor (Q > 2000) for better frequency selectivity and nearly zero temperature coefficient of resonant frequency ('tf) for frequency stability with temperature. In addition to the above characteristics, the..ir low cost of production and excellent integrability to microwave integrated circuits (MICs) make them indispensable components in microwave oscillators, filters, duplexers used in cellular phones and in dielectric resonator antennas. Dielectric resonators increasingly replace the conventional resonators such as metallic cavities or micro strip circuits. Though several temperature-stable DRs are available at present, investigation is still going on to find new materials having better dielectric resonator properties. In this work we investigate the microwave dielectric properties of (1) AsB40ls (A = Ba, Sr, Mg, Ca, Zn; B = Nb, Ta) ceramics, their solid solutions and mixtures (2) MO-La203-Ti02 (M = Ba, Sr, Ca) ceramics which mainly consists ofAnBn- ,03n(n=5, 6, or 8)type cation deficient hexagonal perovskites and (3) a novel methodof achieving temperature compensation by stacking positive and negative 'tf resonators. Dielectric resonator properties were studied in terms ofphases, crystal structure, crystal symmetry, polarisability ofions, lattice parameters and characterization techniques such asXRDand SEM are employed. Chapter 1 is a general introduction about material, scientific and technological aspects of DRs. Three important parameters, er. Q and 'tf, used for the DR characterization are described. The relationship of the above parameters with the fundamental material characteristics isdiscussed. Different modes are excited when a DR is excited with suitable microwave spectrum offrequencies. A description ofanalytical determination offrequencies and construction ofmode charts used for sample design and modeidentification are also discussed. Chapter 2 presents the methods used for the preparation of ceramics and the various techniques used for the microwave characterization ofdielectric properties. The ceramic samples..were prepared through the solid-state ceramic route. The dielectric constant of the ceramics at microwave frequencies are measured using the end shorted dielectric post resonator. The quality factors are determined by a transmission mode cavity. Thetemperature coefficient ofresonant frequency ('tf) is measured by heating the end shorted dielectric post resonator set up in the temperature range 20 to 75°C and by noting thevariation ofthe resonant frequency with temperature. The crystal structure of the samples is analysed using powder X-ray diffraction pattern and surface morphology andgrain sizeisobserved using ScanningElectron Microscopy. Chapter 3 describes the investigation of microwave dielectric properties of AsB (A = Ba, Sr, Mg, Ca, Zn; B = Nb, Ta) ceramics. The ceramics show dielectric 401S constant in the range 11 to 51. The hexagonal perovskites show higher dielectric constants than the orthorhombic phases MgSNb401S and MgsT3401S. The FIR and submillimetertechniques are usedto studythe above compounds. The basic theory ofthe techniques is discussed. An indirect estimation ofthe lower limit ofdielectric loss and upper limit of dielectric constant at microwave frequencies can be obtained by the extrapolation of real part and imaginary part of the dielectric function down to 11