Abstract
X-ray structure determinations of Langbeinite type K2(Cd1-xCox)2(SO4)3, x≅0.02 at three temperatures (440, 540 and 640 K) above the P2 13-P2 12121 transition temperature (434 K) reveal that the M 2+ (M 2+=Cd) ion is displaced from the centre of the octahedron at all temperatures in the cubic phase. Simultaneously the distortion of the oxygen framework decreases with increasing temperature. The structural phase transition occurs when the bond lengths of the six bonds in each of the M 2+ octahedra are all equal, and it is proposed that this equalisation of bond lengths acts as the trigger for the phase transition. The structural deformation of the oxygen sublattice is such that rather regular octahedra around Cd occur at very high temperatures with Cd displaced from the centre. With decreasing temperature the octahedra distort under conservation of the triad, such that the differences between the various bond lengths Cd-O decrease. The phase transition occurs when all bond lengths around the Cd position become equal.
The behaviour of the oxygen framework and the offcentring of the Cd/Co atom combine to produce an increasing distortion with increasing temperature as viewed by the central atom. Thus the interpretation of Optical Spectra, in which an increase in line splitting with temperature was observed, as being due to the off-centring of the Co, is confirmed.
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References
Abrahams SC, Bernstein JL (1977) Piezoelectric langbeinite-type K2Cd2(SO4)3: Room temperature crystal structure and ferroelastic transformation. J Chem Phys 67:2146–2150
Abrahams SC, Lissalde F, Bernstein JL (1978) Piezoelectric langbeinite-type K2Cd2(SO4)3 structure at four temperatures below and one above the 432 K ferroelastic-paraelastic transition. J Chem Phys 68:1926–1935
Devarajan V, Salje E (1986) Phase transitions in langbeinites II: Raman spectroscopic investigations of K2Cd2(SO4)3. Phys Chem Minerals 13:25–30
Dvorak V (1972) Structural phase transitions in langbeinites. Phys Status Solidi (b) 52:93–98
Ikeda T, Yasuda G (1975) The phase transition of ferroelastic Tl2Cd2(SO4)3. Jpn J Appl Phys 14:1287–1290
Lissalde F, Abrahams SC, Bernstein JL, Nassau K (1979) Diffraction and dielectric study of the K2Cd2(SO4)3 paraelastic-ferroelastic phase transition. J Appl Phys 50:845–851
Misra SK, Korczak SZ (1986) Mn2+ EPR study of the phase transition in langbeinite Cd2(NH4)2(SO4)3. J Phys C: Solid State Phys 19:4353–4361
Percival MJL, Salje E (1989) Optical absorption spectroscopy of the P213-P212121 transformation in K2Co2(SO4)3 langbeinite. Phys Chem Minerals 16:563–568
Percival MJL (In Preparation) Optical Spectroscopy of doped materials — the use of transition metals as a probe for the behaviour of cations in minerals
Speer D, Salje E (1986) Phase transitions in langbeinites I: Crystal chemistry and structures of K-double sulfates of the langbeinite type M ++2 K2(SO4)3, M++ =Mg, Ni, Co, Zn, Ca. Phys Chem Minerals 13:17–24
Yamada N, Maeda M, Adachi H (1981) Structures of langbeinitetype K2Mn2(SO4)3 in cubic and orthorhombic phases. J Phys Soc Jap 50:907–913
Zemann A, Zemann J (1957) Die Kristallstruktur von Langbeinit, K2Mg2(SO4)3. Acta Crystallogr 10:409–413
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Percival, M.J.L., Schmahl, W.W. & Salje, E. Structure of cobalt doped K2Cd2(SO4)3 langbeinite at three temperatures above the P213-P212121 phase transition, and a new trigger mechanism for the ferroelastic transformation. Phys Chem Minerals 16, 569–575 (1989). https://doi.org/10.1007/BF00202213
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DOI: https://doi.org/10.1007/BF00202213