Negative thermal expansion (NTE) is exhibited over the entire x range for Cu1.8Zn0.2V2–xPxO7. In particular, dilatometric measurements using epoxy resin matrix composites containing the spray-dried powder demonstrated that the thermal expansion suppressive capability was almost unchanged for x≤0.1. With increasing x, the x-ray diffraction peak position moves systematically, but some peaks are extremely broad and/or asymmetric, suggesting disorder in the internal structure. The crystallographic analysis confirmed NTE enhancement by microstructural effects at least for x=0.2. Preliminary measurements suggest higher resistivity and lower dielectric constant than that of pure vanadate, which is suitable for application to electronic devices.

Because of growing demands for thermal expansion control in a local region, typically inner components of electronic devices, there is currently a great deal of interest in negative thermal expansion (NTE) fine particles. The spray-drying method without grinding produced micrometer-scale fine particles of pyrovanadate Cu 1.8 Zn 0.2 V 2 O 7 showing a large negative coefficient of linear thermal expansion α L ~ -14 ppm/K equivalent to that of the bulk body. The solid-solution system Cu 1.8 Zn 0.2 V 2-x P x O 7 maintains the NTE functionality in a wide x compositional range. Phosphorus substitution contributes to cost reduction and to improvement of electrical insulation. Control of the structural phase transition in the phosphate analog Zn 2 P 2 O 7 by substituting Mg for Zn realized a huge negative α L exceeding -60 ppm/K over a wide temperature range including room temperature. Because small particles are obtainable even with the conventional solid-phase reaction, the 1 μm level fine particles were obtained successfully using the pulverization method without degrading the function. It has high practicality because it is composed only of inexpensive and environmentally friendly elements such as Zn, Mg, and P. These NTE fine particles are expected to support great progress in thermal expansion control engineering.