Formation and properties of crystalline compounds in the Lu2O3-Al2O3 system

The Lu2O3–Al2O3 system: Relationships for equilibrium-phase and supercooled states

“…This is confirmed also by observation that formation of the monoclinic phase Lu 4 Al 2 O 9 takes place at 1650 1C and higher temperatures [6], but the samples treated below the melting point are commonly multiphase and contain in addition 3:5 and Lu 2 O 3 phases. This phase transforms at high temperature annealing into 3:5 and Lu 2 O 3 [11]. Lu 4 Al 2 O 9 , melts incongruently at 2000 1C, above which liquid and Lu 2 O 3 are in equilibrium [6].…”

“…On the other hand, studies of solidification of melts in Ref. [11] have shown that the perovskite phase can be nucleated only when sufficiently high supercooling is present at the solidification point. Thus, it can be concluded that the LuAlO 3 perovskite has a narrow stability range, approximately located at 1750-1930 1C, outside which it decomposes separating the two neighboring phases: Lu 4 Al 2 O 9 and Lu 3 Al 5 O 12 .…”

“…It was observed that in unseeded melts the perovskite phase could be nucleated only if a sufficiently high degree of supercooling was present at the solidification point (see Refs. [11,14] for more details); when formed, the perovskite phase is stable above the spontaneous solidification point and melts at $1900 1C [12]. It has been also shown that the ability of melts to undergo supercooling is governed by the overheating temperature and the time of heating in the molten state [13,14].…”

“…Further studies [11][12][13][14] employing the vertical Bridgman process in argon/hydrogen atmosphere have shown that high quality LuAlO 3 single crystals can be obtained under conditions near to equilibrium. It was observed that in unseeded melts the perovskite phase could be nucleated only if a sufficiently high degree of supercooling was present at the solidification point (see Refs.…”

“…In this respect, compounds existing in the Lu 2 O 3 -Al 2 O 3 system are most attractive, since they include large amounts of heavy lutetium and are transparent in the UV range of emission of rare-earth luminescent ions, such as Ce 3+ or Yb 3+ . One of them, lutetium aluminum perovskite doped with trivalent cerium (LuAlO 3 -Ce 3+ , LuAP) possessing high density (8.34 g/cm 3 ), high photoelectric fraction (32.1% for 511 keV), fast decay (18 ns) and relatively high light yield (11,400 ph/MeV) is one of the prime scintillator materials for next generation positron emission tomography (PET). The crystal clear collaboration (CCC) [3] has developed small animal PET scanners called Clear PET, which employ LuAlO 3 and similar crystals.…”