Anomalous increase in specific volume upon crystallization of some alloys in the zirconia–yttria–erbia system

New inorganic materials with dominant ionic chemical bonds which expand upon crystallization at room temperature have been discovered. This effect has been observed in alloys of the ZrO2–Y2O3–Er2O3 system. It can be interpreted as transition existence from crystal structure with dominant ionic bonds to the one with dominant covalent or covalent-metallic bonds while heating below the melt point. So the phase transition from cubic C phase to hexagonal H which occurs in these materials at about 2300 °C should be linked to changing in the dominant type of chemical bonds. phenomenon should be take place upon oxides crystallization of rare-earth elements which have physicochemical properties and electron structure similar to those of Y2O3, namely of heavy lanthanides oxides Ho2O3, Tm2O3, and Yb2O3; upon the crystallization of their alloys with each other and with Er2O3 and Y2O3.