Resource efficient development of combinatorial materials for future Multilayer Ceramic Capacitor applications

This thesis investigates the permittivity-temperature (εr-T) profiles of individual dielectric materials through simulation led experiments. The results are used to assess the capability of using layered ceramic systems to meet the Temperature Coefficient of Capacitance (TCC) requirements of Multi-Layer Ceramic Capacitors. The layered ceramics exceed the performance of existing BaTiO3 (BT) based materials, especially at high temperatures (>125 oC). The application of simulations reduces the need for experimental research, accelerating the discovery of new material combinations of interest.
Combining dielectric layers in a series combination has the following benefits over materials currently used commercially:
(a) Literature reported εr-T data can be used directly as input data.
(b) Individual materials can exhibit highly temperature dependent εr-T data.
(c) Materials do not require heterogeneous microstructures to be viable.
(d) New material combinations do not require extensive and iterative experimental research.
(e) Simulations can effectively predict novel material combinations of interest.
(f) Changes to performance criteria demands (operating temperature range, TCC (%), εRT) are easily accommodated.
(g) The electrical connectivity of the material layers is controlled by the user and not dependent on processing conditions.
Ternary layer systems using 9 NaNbO3-BaTiO3 (NNBT) εr-T profiles as input data can be optimised to meet X9P classification (-55 to 200 oC, TCC < ±10%). This performance is beyond the capability of existing commercial BT-based materials and required a high Tmax (peak in εr-T profile) material layer which is only achieved at high NN contents.
Tetragonal Tungsten Bronze (Ca,Sr,Ba)Nb2O6 materials were investigated as high Tmax materials, with selected compositions displaying a Tmax range from 62 to 382 oC achieved by altering the A-site cations. The large temperature range of TCC stability from 25 to 400 oC (TCC < ±22%), demonstrates the potential of these layered ceramic systems to significantly progress the performance of MLCC devices.