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6H 1733 K P63/mmc (194) Z = 6 non-ferroic metastable at 300 K if cooled rapidly; stabilized by certain impurities.
I 1733-403 K Pmm (221) Z = 1 non-ferroic Type = CaTiO3 idealized. May exist up to melting if phase 6H is not stabilized.
II 403-278 K P4mm (99) Z = 1 ferroelectric, ferroelastic 6 ferroelectric, 3 ferroelastic variants.
III 278-183 K Amm2 (38) Z = 2 ferroelectric, ferroelastic 12 ferroelectric, 6 ferroelastic variants.
IV <183 K R3m (160) Z = 3 ferroelectric, ferroelastic 8 ferroelectric, 4 ferroelastic variants.
I 434 K Fmm (225) Z = 4 non-ferroic Type = K2PtCl6. Decomposes above 590 K.
II 434-400 K P4/mnc (128) Z = 2 ferroelastic 3 variants.
III < 400 K P21/n (14) Z = 2 ferroelastic 12 variants.
I I4/mcm (140) Z = 4 non-ferroic structure not yet unambiguously determined.
II 670-360 K I4/m (87) Z = 4 ferroic* 2 variants differing in elastic properties.
III 360-320 K I2/c (15) Z = 4 ferroelastic 4 variants.
IV 320-270 K P4/n (85) Z = 8 ferroic* antiferroelectric. *As in phase II.
V < 270 K I4cm (108) Z = 4 ferroelectric 2 variants.
I 1423 K tetragonal - nonferroic metastable from 1423 to 873 K if cooled rapidly.
II <873 K Bb21m (36) Z = 40 ferroelectric metastable at room temperature if cooled rapidly from > 1423 K.
III <1423 K R3m (160) Z = 9 non-ferroic the stable phase at all temperatures below 1423 K.
<0.8 GPa P41212 (92) Z = 4 non-ferroic room temperature structure determination.
0.8 GPa P21212 (19) Z = 4 ferroelastic 2 variants, room-temperature structure determined at 2 GPa.
2400-1720 K P63mc (186) or P63/mmc (194) Z = 2 non ferroic Type = K2SO4 high. Stable.
-H 1720-1430 K Pcmn (62) Z = 4 ferroelastic Type = K2SO4 low. Stable.
-L 1430-950 K Ccm21* (36) Z = 16 - Type = K2SO4 low, slightly deformed. Stable. *Other space groups are possible.
<950 K P21/n (14) Z = 4 - Type = K2SO4 low, strongly deformed. Metastable with respect to .
<1000 K Pcmn (62) Z = 4 - Type = olivine. Stable.
1663 K Imm (229) Z = 2 non-ferroic Type = W. Melting at 1808 K.
1663-1183 K Fmm (225) Z = 4 non-ferroic Type = Cu.
1183-1043 K Imm (229) Z = 2 paramagnetic Type = W.
<1043 K Imm (229)* Z = 2 ferromagnetic Type = W. *Magnetic structure is pseudocubic.
13 GPa P63/mmc (194) Z = 2 - Type = Mg.
- 46 GPa Fmm (225) Z = 4 non-ferroic Type = Cu.
- 46-26 GPa P63/mmc (194) Z = 4 non-ferroic Type = Nd .
- 26-12 GPa Rm (166) Z = 9 - Type = Sm .
- <12 GPa P63/mmc (194) Z = 2 - Type = Mg.
This example is chosen to illustrate a situation in which the phase diagram is an intricate function of temperature and pressure. The proposed notation specifies a rectangular (T, p) area for each phase, approximately superimposed on the actual range of the phase. Such a rough indication is generally insufficient to reconstruct, even approximately, the shape of the phase diagram. However, it provides the approximate stability range for the various phases and may be considered a first step in their identification. Only the three phases with identified crystal symmetries are listed below (labelled I, II, III in the published diagram) and only the first three fields of the nomenclature are entered:
I 900-670 K; <3 GPa cubic
II 670-500 K; <0.8 GPa cubic
III 500-270 K; <0.5 GPa orthorhombic .
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