Abstract: A capacitive energy storage device is provided utilizing a ferroelectric pyrochlore ceramic material as the dielectric. The preferred ceramic material has the formula:(Cd.sub.1-x Pb.sub.x).sub.2 (Nb.sub.1-y Ta.sub.y).sub.2 O.sub.7,where x and y are numbers in the range of from 0 to 1. Other ceramic materials used in the invention are the non-pyrochlore ceramic material (Sr.sub.1-a Ba.sub.a)TiO.sub.3 or the non-pyrochlore ceramic material (Pb.sub.1-b Ni.sub.b).sub.3 MgNb.sub.2 O.sub.9. These ceramic materials exhibit large dielectric constants at temperatures in the range of 50.degree.-90.degree. K.

Abstract: Capacitive pressure and temperature sensing devices for use at cryogenic temperatures are provided utilizing a quantum ferroelectric pyrochlore ceramic material as the dielectric. The ceramic material has the formula:(Cd.sub.1-x M.sub.x).sub.2 (Nb.sub.1-y M'.sub.y).sub.2 O.sub.7where M is Pb, Ca, Sr, Ba, or mixtures thereof; where M' is Ta, Sb, or mixtures thereof; and where x and y are numbers in the range of from 0 to 1. M and M' are chosen such that the pressure sensing device uses a ceramic with a nearly temperature independent dielectric constant while the temperature sensing device uses a ceramic with a strongly temperature dependent dielectric constant. The sensors may comprise multi-layered capacitive devices, and may be combined into a single temperature and pressure sensing device.