Ba(Ti 1-x Zr x ) 2 O 5 Ceramics Prepared by Aerodynamic Levitation

Transcription

1 11 th Korea-Japan Joint Seminar on Space Environment Utilization Research July 24 th The University of Tokyo, Tokyo, Japan Ba(Ti 1-x Zr x ) 2 O 5 Ceramics Prepared by Aerodynamic Levitation Won-Seung Cho, Chi-Hoon Lee, Chi-Hwan Lee, Shinichi Yoda Inha university, School of Material Science and Engineering JAXA

2 Contents Introduction Theoretical background & Objective Experimental procedure Results of Ba(Ti 1-x Zr x ) 2 O 5 Conclusion

3 1. Introduction Containerless levitation technique? Materials are no longer in physical contact with any container. Containerless processing can prevent melt contamination, minimize heterogeneous nucleation. Fig. 1. Comparison of conventional container melting and containerless melting method.

4 1. Introduction Aerodynamic Electrostatic Acoustic Electromagnetic Fig. 2. Typical containerless levitation methods

5 2. Theoretical background Characteristics of BaTi 2 O 5 Giant permittivity at metastable α-phase(~10 7 ) Lead free ferroelectric materials with high Curie temperature Giant second harmonic generation Structure of BaTi 2 O 5 (TiO 6 ) Fig. 3. Ti 4+ coordination(tio 5 ) in BaTi 2 O 5 glass and α-phase.

6 2. Theoretical background & objective Dr. Yono, Dr Yoda developed new optical materials with high refractive index(n>2.0). centrosymmetric geometry Non-centrosymmetric geometry TiO 4 coordination TiO 6 coordination TiO 5 coordination Conventional Ti-O coordination New Ti-O coordination Objective: Investigate the effect of Zr on the optical properties of BaTi 2 O 5.

7 3. Experimental procedure BaCO 3 TiO 2 ZrO 2 Ball-milling Drying Granulation in ethanol, for 12h (ZrO 2 ball) Stirring at 80 Sieving (<50mesh) Forming Pre-Sintering Uniaxial pressing 1100, 12h Aerodynamic Levitation

8 3. Experimental procedure Fig. 4. Photograph of aerodynamic levitator

9 3. Experimental procedure Aerodynamic levitation process CO 2 LASER Diode Pointer Mirror (Au coated) CCD & HSV Camera One-color Pyrometer Fused Silica ZnSe (AR coated) Sample MFC O 2 Conical Nozzle

10 3. Experimental procedure Table 1. Composition used in this sturdy. Ba(Ti 1-x Zr x ) 2 O 5 x X < BaO-TiO 2 -ZrO 2 phase diagram. Ref) G. H. Jonker and W. Kwestroo, The Ternary Systems BaO-TiO 2 -SnO 2 and BaO-TiO 2 -ZrO 2, Journal of The American Ceramic Society, 41(10), (1957)

11 3. Experimental procedure Characterization of levitated sample Time-temperature profile (one color pyrometer) In-situ observation of molten droplet (High speed camera) Density (Archimedes method) Thermal analysis (DSC) Phase identification (Room and High temperature XRD) Microstructure (SEM) Dielectric property (Permittivity) Optical property (Refractive index) Determination of spectral emissivity Wien s approximation to Planck s law 1 1 λ - = ln(ε λ ) T T C ε =exp T -T ε 0.92ε λ m A(m) λ A material C λ T : True temperature (K) T A : Apparent temperature (K) λ : Wavelength of Si (0.9 μm) C 2 : Planck s second radiation const. (1.4388x10-4 μm K) ε λ : Spectral emissivity (transmittance of fused silica: 0.92)

12 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 Transparent Translucent Opaque Fig. 5. Photographs of a levitated BaTi 2 O 5 samples. The sample changed from transparent to opaque with increasing sample mass. Fig. 6. Schematic temperature-time profile for BaTi 2 O 5 during aerodynamic levitation. T M, T N, ΔT S and ΔT R denote the melting temperature, onset temperature of nucleation, undercooling level and degree of recalescence, respectively.

13 Temperature ( o C) 4. Results of Ba(Ti 1-x Zr x ) 2 O Time (s) 473 /s 0.5mm Fig. 7. Temperature-time profile of BaTi 2 O 5 sample (25mg) and Snap shot images of the molten droplet.

14 Temperature ( o C) 4. Results of Ba(Ti 1-x Zr x ) 2 O Melt(Liquid) Undercooled(L) L+S S /s Under cooling stage Recalescence Cooling stage Time (s) 0.5mm Fig. 8. Temperature-time profile of BaTi 2 O 5 sample (59 mg) and Snap shot images of the molten droplet.

15 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 Transparent Translucent Opaque 1mm x=0.3 x=0.4 x=0.5 Fig. 9. Photographs of a levitated Ba(Ti 1-x Zr x ) 2 O 5 samples with a diameter of ~2.0 mm and mass of 30 mg.

16 Intensity(a.u.) 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 x=0.5 ZrO 2 Ba 2 Ti 5 O 12 Ba(Ti,Zr)O 3 x=0.4 x=0.3 x=0.2 x= theta Fig. 10. XRD patterns of as-levitated Ba(Ti 1-x Zr x ) 2 O 5 samples.

17 Heat flow (a.u.) 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 T p1 : 727 Metastable α-phase BaTi 2 O 5 Ba(Ti 0.9,Zr 0.1 ) 2 O 5 T p1 : 743 Metastable α-phase T p2 : 842 Stable γ-phase T p2 : 765 Metastable β-phase Temperature ( o C) Fig. 11. DSC curves of the as-levitated BaTi 2 O 5 and Ba(Ti 0.9 Zr 0.1 ) 2 O 5 samples.

18 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 Table 2. Thermophysical properties of the as-levitated BaTi 2 O 5 and Ba(Ti 0.9 Zr 0.1 ) 2 O 5 sample. T g ( ) T x1 ( ) T ( ) (T x1 -T g ) T p1 ( ) T x2 ( ) T p2 ( ) T m ( ) BaTi 2 O Ba(Ti 0.9 Zr 0.1 ) 2 O T g : Glass transition temperature T x1 : 1 st crystallization onset temperature T p1 : 1 st crystallization peak temperature T x2 : 2 st crystallization onset temperature T p2 : 2 st crystallization peak temperature T(T x1 - T g ): Thermal stability T m : melting temperature

19 Intensity(a.u.) Intensity(a.u.) 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 (a) 1280 o C γ-bati 2 O 5 β-bati 2 O 5 α-bati 2 O 5 (b) 1280 o C Ba(Ti,Zr)O 3 Ba 2 Ti 5 O 12 γ-bati 2 O 5 α-bati 2 O o C 900 o C 880 o C 827 o C 827 o C 742 o C 797 o C 722 o C 737 o C 27 o C 27 o C theta theta Fig. 12. High temperature XRD patterns of (a)bati 2 O 5 sample and (b) Ba(Ti 0.9 Zr 0.1 ) 2 O 5.

20 Increasing Temperature 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 Stable γ-phase Metastable β-phase Phase decomposition (3BaTi 2 O 5 BaTiO 3 +Ba 2 Ti 5 O 12 ) Stable γ-phase Metastable α-phase Metastable α-phase Amorphous Amorphous BaTi 2 O 5 Ba(Ti 0.9 Zr 0.1 ) 2 O 5 Fig. 13. Phase transition behavior in BaTi 2 O 5 and Ba(Ti 0.9 Zr 0.1 ) 2 O 5.

21 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 (X<0.1) Translucent Transparent 2mm x= Fig. 14. Photographs of a levitated Ba(Ti 1-x Zr x ) 2 O 5 samples with a diameter of ~2.0 mm and mass of 30 mg.

22 Heat flow (a.u.) 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 (X<0.1) Temperature ( o C) Fig. 15. DSC curves of Ba(Ti 1-x Zr x ) 2 O 5 (x=0, 0.001, 0.02, 0.04, 0.06 and 0.08) x=0

23 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 (X<0.1) Table 3. Thermophysical properties of the as-levitated BaTi 2 O 5 and Ba(Ti 1-x Zr x ) 2 O 5 (X<0.1) samples. x T g T x1 T p1 T x2 T p2 T x1 -T g T g : Glass transition temperature T x1 : 1 st crystallization onset temperature T p1 : 1 st crystallization peak temperature T x2 : 2 st crystallization onset temperature T p2 : 2 st crystallization peak temperature T x1 - T g : Thermal stability

24 Permittivity Permittivity 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 (a) khz 1 khz 10 khz 100 khz (b) khz 1 khz 10 khz 100 khz Temperature( o C) Temperature( o C) 827 Fig. 16. Temperature dependence of permittivity for (a) BaTi 2 O 5 and (b) Ba(Ti 0.92 Zr 0.08 ) 2 O 5

25 4. Results of Ba(Ti 1-x Zr x ) 2 O 5 Table 5. Density (ρ), refractive index (n d ) at nm, Abbe number (ν d ) for Ba(Ti 1-x Zr x ) 2 O 5. x Density Abbe number, refractive index D n n F n D : refractive index at nm n F : refractive index at nm n C : refractive index at nm D 1 n Abbe number C

26 5. Conclusions (1) Ba(Ti 1-x Zr x ) 2 O 5 (BTZO) samples were prepared by aerodynamic levitation. The effects of Zr on the BaTi 2 O 5 were investigated. 1. Colorless, transparent BTZO samples were successfully prepared at Zr content, X=0.04~0.1 without adding network-forming agent such as SiO 2. On the other hand, BTZO sample was translucent due to devitrification at X=0.2, and opaque due to crystallization at higher Zr content more than x= With increasing temperature, amorphous BaTi 2 O 5 was changed into metastable α-phase metastable β-phase stable γ-phase, whereas amorphous Ba(Ti 0.9 Zr 0.1 ) 2 O 5 was changed into metastable α-phase stable γ-phase. Finally, γ- phase was decomposed into BaTiO 3 and Ba 2 Ti 5 O 12.

27 5. Conclusions (2) 3. When BaTi 2 O 5 was transited from amorphous to metastable α-phase, permittivity of the sample increased dramatically, showing giant permittivity (~10 7 at 0.1 khz). In BTZO samples, the temperature range for the giant permittivity became wider with Zr 4+ content. It was ascribed to increased thermal stability of metastable α- phase. 4. Transparent BTZO samples represented higher refractive index more than 2.0 and high Abbe number. The samples developed in this study can be utilized for high-performance optical lens, etc.

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29 High refractive index glasses are essential components of lenses and enable the realization of high power and high resolution as well as wide viewing angles for digital cameras and microscopes. Therefore, the development of new glass compositions with higher refractive indices is of great interest to glass manufacturers. Greater wavelength dispersion results in smaller values of νd. The value of νd generally decreases when the value of nd increases. This means that high refractive index glasses typically exhibit large wavelength dispersion. Glasses with values nd 2 and νd 20 are desired materials for high-valued lenses; however, very few commercial glasses with these properties are currently available.

30 Fig. Phase diagrams of the BaO-TiO 2 binary system reported by Rase and Roy(a) and Zhu and West(b).