Hydrothermal Ba x Sr 1-x TiO 3 Powders for Multilayer Capacitors

1. Hydrothermal BaxSr1-xTiO3 Powders for Multilayer Capacitors Prof. Elliott Slamovich Matt Slone

2. Project Objectives • Hydrothermal production of BaxSr1-xTiO3 powders • Tape cast powders to form thin films • Fabricate MLCCs from films • Test dielectric properties of films and capacitors

3. Review • Capacitors • BaxSr1-xTiO3 ceramics • Tape casting

4. Capacitors • A capacitor is a device used to store potential energy in an electric field • Typical capacitors consist of two conducting plates separated by a dielectric material • Energy is stored as a result of the shifting of ions in the dielectric acting to oppose an applied electric field. Diagram: Callister, Materials Science and Engineering An Introduction, 5th ed. 2000.

5. Multilayered Ceramic Capacitors • In parallel-plate capacitors C = oA / d • For greatest capacitance, increase area and decrease thickness • Capacitor size can be conserved by stacking many very thin capacitors

6. BaTiO3 / SrTiO3 Ceramics • Both have perovskite crystal structure, allowing the formation of a solid solution • Have very high dielectric constants at their Curie Temperatures • The curie temperature of the BaxSr1-xTiO3 can be controlled by the Ba / Sr ratio in the solid solution • Tc of BaTiO3 is 120oC, Tc of SrTiO3 is –50oC

7. Tape Casting • Process to form thin, uniform sheets of ceramic material • Ceramic powder mixed into an slurry containing solvent, binder, and dispersant. • Slurry is cast into a soft, flexible green tape • Solvent evaporation, binder burnout, and sintering are performed to obtain solid ceramic material Diagram: Mistler; Twiname, Tape Casting Theory and Practice, 2000.

8. Powder Production • BaxSr1-xTiO3 powders produced using a hydrothermal process • Reactions performed with solution properties: • The ratio (Ba + Sr) / Ti = 2 • (Ba +Sr) concentration of 0.8M • NaOH concentration of 1M • Typical yield of about 30g of powder from 500ml of solution

9. Powder XRD

10. Slip Composition • Wt % • 60.70 • 0.61 • 13.40 • 13.40 • 8.09 • 3.79 • Function • Ceramic • Dispersant • Solvent • Solvent • Binder • Plasticizer Component BaxSr1-xTiO3 powder Hypermer KD-1 Methyl Ethyl Ketone Ethanol Acryloid B-72 Butyl Benzyl Phthalate

11. Tape Casting • Each of the final four powders was tape cast with a doctor blade height of 300 m • Green tape thickness ranged from 110 m to 135 m • Thickness varied up to 25 m for a given tape

13. Laminating • Tapes were cut using a circular die 25 mm in diameter • Circles were stacked to a thickness of about 1.5 mm • Stacks were pressed in the die at a pressure of 18 MPa and a temperature of 230oF

15. Binder Burnout and Sintering • Binder burnout attempted on laminates at 420oC for 2 hours with a ramp of 15oC / hr • Each of the samples cracked during the process

16. Successes • Hydrothermal process adapted to suit production needs • Slip composition for the tape casting of hydrothermally produced BaxSr1-xTiO3 was developed • Tape casting and laminating procedure was determined

17. Further Studies • Refine binder burnout procedure • Examine sintering of laminates • Examine dielectric properties of laminates

18. Acknowledgements • Prof. Elliott Slamovich • Jacob Jones • Huiwen Xu • Dave Roberts