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

Project Objectives Hydrothermal production of Ba x Sr 1-x TiO 3 powders Tape cast powders to form thin films Fabricate MLCCs from films Test dielectric properties of films and capacitors

Review Capacitors Ba x Sr 1-x TiO 3 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, 5 th ed

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

BaTiO 3 / SrTiO 3 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 Ba x Sr 1-x TiO 3 can be controlled by the Ba / Sr ratio in the solid solution T c of BaTiO 3 is 120 o C, T c of SrTiO 3 is –50 o C

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 Ba x Sr 1-x TiO 3 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 Ba x Sr 1-x TiO 3 powder Hypermer KD-1 Methyl Ethyl Ketone Ethanol Acryloid B-72 Butyl Benzyl Phthalate Wt % Function Ceramic Dispersant 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 230 o F

Binder Burnout and Sintering Binder burnout attempted on laminates at 420 o C for 2 hours with a ramp of 15 o C / 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 Ba x Sr 1-x TiO 3 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