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High temperature single crystal investigation in a clinopyroxene of composition Na0.50Ca0.50Cr0.50Mg0.50Si2O6
No full textThe high-pressure C2/c -P21/c phase transition along the LiAlSi2O6 - LiGaSi2O6 solid solution
No full textHigh temperature single crystal investigation in a clinopyroxene of composition (Na0.5Ca0.5)(Cr0.5Mg0.5)Si2O6
No full text
Synthesis, TEM characterization and thermal behaviour of LiNiSiO pyroxene
Full text linkA pyroxene with composition LiNiSiO was synthesized at T = 1,473 K and P = 2.0 GPa; the cell parameters at T = 298 K are a = 9.4169(6) Å, b = 8.4465(7) Å, c = 5.2464(3) Å, β = 110.534(6)°, V = 390.78(3) Å. TEM examination of the LiNiSiO pyroxene showed the presence of h + k odd reflections indicative of a primitive lattice, and of antiphase domains obtained by dark field imaging of the h + k odd reflections. A HT in situ investigation was performed by examining TEM selected area diffraction patterns collected at high temperature and synchrotron radiation powder diffraction. In HTTEM the LiNiSi O was examined together with LiCrSiO pyroxene. In LiCrSiO the h + k odd critical reflections disappear at about 340 K; they are sharp up to the transition temperature and do not change their shape until they disappear. In LiNiSiO the h + k odd reflections are present up to sample deterioration at 650 K. A high temperature synchrotron radiation powder diffraction investigation was performed on LiNiSiO between 298 and 773 K. The analysis of critical reflections and of changes in cell parameters shows that the space group is P-centred up to the highest temperature. The comparative analysis of the thermal and spontaneous strain contributions in P2/c and C2/c pyroxenes indicates that the high temperature strain in P-LiNiSiO is very similar to that due to thermal strain only in C2/c spodumene and that a spontaneous strain contribution related to pre-transition features is not apparent in LiNiSiO. A different high-temperature behaviour in LiNiSiO with respect to other pyroxenes is suggested, possibly in relation with the presence of Jahn-Teller distortion of the M1 polyhedron centred by low-spin Ni
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