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Novel synthesis and manufacturing routes for functional materials and devices

Synthesis of novel powder morphologies

Materials engineers are responsible for the research, specification, design and development of materials to advance technologies of many kinds. Here at Sheffield, we develop novel biotemplated synthesis to control the crystal morphology of complex oxides, and to lower the reaction temperatures, thus allowing energy to be saved over the standard synthetic techniques and producing bulk quantities of electroceramic materials with novel morphologies.

Fabrication of novel dielectric substrates

Furthermore, we investigate new methods for fabrication of Aluminium substrates with dense and homogeneous insulating surface layers comprising nanocrystalline ceramics to achieve a simultaneous enhancement in dielectric strength and thermal conductivity, which could be used in high brightness light emitting diodes.

Substitution of toxic and scarce raw materials in materials and devices

One of the great challenges in functional materials community is to eliminate scarce and environmentally unfriendly elements. Nowhere is this drive more pertinent than in the sensor, capacitor and transducer industries which rely on lead zirconate titanate and rare earth doped barium titanate for many applications. It is paramount therefore that new PbO free compositions are generated for sensor and transducer applications and rare earth free barium titanate compositions are developed for multilayer ceramic capacitors.

Novel low temperature synthesis

Synthesis

Biotemplated synthesis is a powerful way to control the crystal morphology of complex oxides, and to lower the reaction temperatures, thus allowing energy to be saved over the standard synthetic techniques.

Biotemplates are polymeric materials found in nature, for example long chain sugar molecules or the structural polysaccharides found in seaweed. The structures of the polymers are such that they are able to uptake and spatially separate metal cations and therefore influence the structure of the final oxide material.

Many different crystal forms can be accessed in this way, including nanoplates, nanowires, and nanostructured foams, and these templates can also be used to influence the macroscale structure of the materials, for example in the formation of micron scale spheres.

SUBST is concerned with the use of these and similar templated techniques to produce bulk quantities of electroceramic materials with novel morphologies. 

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Manufacturing routes to sustainability in LEDs

High Brightness Light Emitting Diodes (HB-LEDs) may provide compact, energy efficient and long-lasting alternatives to powerful incandescent bulbs, consuming scarce metals such as tungsten.

Successful operation of HB-LEDs relies upon careful thermal management in the metal-backed printed circuit board (below left). In particular, thin dielectric layer separating electrical circuit from the metal substrate, should combine high thermal conductivity and dielectric strength.

Within SUBST we investigate new methods for fabrication of Al substrates with dense and homogeneous insulating surface layers comprising nanocrystalline ceramics to achieve a simultaneous enhancement in dielectric strength and thermal conductivity (below right).

HB-LEDs

Dielectric strength and thermal conductivity

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PbO-free piezoelectric materials and devices

The figures below show two PbO free piezoelectric ceramics developed at Sheffield. The first is based on potassium sodium niobate (KNN) and the second on potassium bismuth titanate (KBT). These formulations will now be utilised to manufacture prototype components and devices in collaboration with our industrial sponsors.

PbO

RE free X7R formulations for multilayer ceramic capacitors

X7R multilayer ceramic capacitors (MLCCs) must maintain +/-15 % of room temperature capacitance between -55 to +125 oC. Most rely on RE ions such as Dy3+ to control the temperature stability and lifetime. By 2020, 3 trillion multilayer ceramic capacitors will be made each year, but supplies of Dy2O3 will run short in the next few years. Dy3+ acts as an acceptor or a donor dopant depending whether it sits on the A or B-site. In the figures to the left BaTiO3 has been doped with NaNbO3. In this case Na+ is the acceptor on the A-site and Nb5+ is the donor on the B-site. Compositions show promising temperature stability but there is much work to do if we are to consider BaTiO3 – NaNbO3 ceramics as genuine contenders for MLCCs.

X7R

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