Part 1 The invention uses a special hemispherical-shape disk made out of piezo-electric material recently developed. One of the faces of the ceramic piezo-electric disk has been chemically reduced during the forming of the ceramic. This reduction imparts the hemispheric shape to the disk when the disk is at rest, i.e. when no electric input is supplied. Application of an electric input causes an electric field between the faces of the disk, and in response the hemispherical shape of the disk changes. Depending on the polarity of the applied electric field the hemispherical shape either flattens or heightens. Part 2 of the invention is a new type Sterling cycle refrigerator. Sterling-cycle refrigerators operate on a closed thermodynamic regenerative cycle with isothermal compression and expansion of the working fluid at different temperature levels. As an integral part of Sterling-cycle cryogenic refrigerators pump devices are needed. The new piezo-electric pump device of part 1 of the invention is used in the new refrigerator as a high-performance compressor and expander pump. To further improve the new refrigerator performance, the invention also features a displacement boost transfer pump to optimise heat exchanger performance. External inputs to the displacement pump are used to control whether at any one time laminar or turbulent flow exists in the heat exchangers for additional improved heat exchanger performance. NASA Tech Brief. 8.5" x 11"