Hydrothermal Ba x Sr 1-x TiO 3 Powders for Multilayer Capacitors Prof. Elliott Slamovich Matt Slone.

Hydrothermal BaxSr1-xTiO3 Powders for Multilayer Capacitors

Prof. Elliott SlamovichMatt Slone

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

Review

• Capacitors

• BaxSr1-xTiO3 ceramics

• Tape casting

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.

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

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

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.

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

Powder XRD

Slip Composition

Component BaxSr1-xTiO3 powder

Hypermer KD-1

Methyl Ethyl Ketone

Ethanol

Acryloid B-72

Butyl Benzyl Phthalate

Wt %

60.70 0.61 13.40 13.40 8.09 3.79

Function Ceramic Dispersant Solvent Solvent Binder Plasticizer

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

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

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

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

Further Studies

• Refine binder burnout procedure

• Examine sintering of laminates

• Examine dielectric properties of laminates

Acknowledgements

• Prof. Elliott Slamovich

• Jacob Jones

• Huiwen Xu

• Dave Roberts