Phase transition behavior of yttria-stabilized zirconia from tetragonal to monoclinic in the lanthanum zirconate/yttria-stabilized zirconia coupled-system using molecular dynamics simulation

Molecular dynamics and experimental study has been carried out to investigate the phase transition behavior in coupled lanthanum zirconate/yttria stabilized zirconia (LZ/YSZ) system. Molecular dynamics (MD) study shows that a tetragonal (t) to monoclinic (m) phase transition behavior of yttria-stabilized zirconia (YSZ) was induced by the lanthanum zirconate (LZ) in the coupled LZ/YSZ system. From an analysis of MD simulations of cooling the coupled LZ/YSZ system down from 1473 K to 1273 K, a volume expansion occurs on the volume change curve, which implies the t to m phase transition in YSZ occurs. In the same condition, however, no trace of volume expansion appears on the cooling curve of single t-YSZ. The simulation results show that the cooling rate significantly affected the phase transition in LZ/YSZ coupled system. The volume expansion in coupled LZ/YSZ at slow cooling rate (0.8 K/ps) was found more significant. The radial distribution functions (RDFs) based on the cations (Zr, Y and La ions) in LZ and YSZ, the technique of tracing cluster based on the cluster type index method (CTIM), the X-ray diffraction (XRD) and the transmission electron microscope (TEM) have been used to confirm simulation results. It is also found that the Y ion loss from YSZ in the coupled-system may be an important reason for t-YSZ to m-YSZ phase by the results of simulation of MD.