The two-step phase transition of titanite, CaTiSiO5: a synchrotron radiation study

Kek, S.; Aroyo, M. I.; Bismayer, U.; Schmidt, Claudia; Eichhorn, K.; Krane, H.‐G.

doi:10.1524/zkri.1997.212.1.9

Cited by 45 publications

(81 citation statements)

References 16 publications

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“…At this state the Ti 4+ atoms are shifted to an off-centered position within the TiO 6 octahedra (same direction within a single chain, but opposite between two adjacent chains) generating an antipolar ordering [1][2][3][4][5][6]. A thermally induced phase transition from space group P2 1 /c ↔ C2/c occurs at temperatures near 500 K. As a result, the between different TiO 6 octahedra chains coherent offcenter displaced Ti atoms decouple accompanied by a shift of the Ca atoms.…”

Section: Introductionmentioning

confidence: 99%

“…A thermally induced phase transition from space group P2 1 /c ↔ C2/c occurs at temperatures near 500 K. As a result, the between different TiO 6 octahedra chains coherent offcenter displaced Ti atoms decouple accompanied by a shift of the Ca atoms. This displacive phase transition has been extensively investigated in synthetic titanite (CaTiSiO 5 ) and highly crystalline titanite close to its end-member composition among others by X-ray diffraction (XRD), optical birefringence, Raman and infrared (IR) spectroscopy [1][2][3][4][5][7][8][9]]. An additional decoupling of the off-centered displaced Ti atoms in the same chain occurs near 825 K during an isosymmetrical phase transition [3][4][5][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase

Beirau¹

2014

Zeitschrift Für Kristallographie - Crystalline Materials

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The present review will give a brief overview mainly focused on studies during the past 5 years on the mineral titanite (end-member composition CaTiSiO 5 ) which could incorporate radioactive elements in its crystal structure. Aspects of investigations were the structural damage resulting from the radioactive decay, the thermally induced recrystallization process and the elastic properties of the mineral. During the radiation induced damage process, namely the metamictization, titanite becomes partially amorphous with coexisting defect enriched crystalline and aperiodic regions. Within these crystalline regions a P2 1 /c to C2/c phase transition (∼ at 500 K) occurs. Resulting from radiation induced structural damage, titanite shows elastic properties close to those of titanite glass. During recrystallization on annealing an initial softening of the titanite structure takes place (up to temperature ∼950 K) resulting from the formation of soft interfaces. Thermal annealing at higher temperatures leads to increasing structural order and the hardening of the mineral.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase

Beirau¹

2014

Zeitschrift Für Kristallographie - Crystalline Materials

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“…Pure titanite crystallizes with the space group P2,/a ( Z = 4) and lattice parameters u = 7.069(2), b = 8.722(5), c = 6.566(8) A and /3 = 113.86(2)0 (Speer and Gibbs, 1976) at room temperature. With increasing temperature or pressure, titanite shows structural phase transitions which have been studied in much detail (Taylor and Brown, 1976;Higgins and Ribbe, 1976;Ghose et al, 1991; Van Heurck et a/., 1991; Bismayer et a/., 1992; Salje et al, 1993;Zhang et al, 1995;Kunz et al, 1996;Meyer et al, 1996;Kek et al, 1997;Chrosch et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Dehydration and recrystallization of radiation-damaged titanite under thermal annealing

Salje¹,

Zhang²,

Groat³

2000

Phase Transitions

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Dehydration of oriented sections of a radiation-damaged titanite crystal, CaTiSi05, at temperatures up to 1500K was analysed using infrared spectroscopy. The IR spectra of the untreated sample show only a very weak orientational dependence. The absence of sharp absorption peaks at wavenumber near 3486 at-' in metamict titanite shows that the local environmental configurations of OH species in the metamict titanite differ strongly from that of crystalline titanite. The OH spectra of radiation-damaged titanite can be decomposed into two components: the first componeut shows anisotropic and sharp spectral features while the second component consists of a broad spectral feature like those observed in disordered silica glasses. It is proposed that the first component is related to the crystalline part of the titanite sample while the second is from the defected and disordered part which suffered strong radiation damage. With increasing annealing temperature, a decrease in the broad absorption between 2500 and 3200~11-l is accompanied by a recovery of sharp IR bands near 3486cm-I which display the same orientational dependence as undamaged single crystals. Annealing the sample at 1000 K leads to the line profiles and orientational dependence of the main OH stretching bands near 3486 cm-l that are virtually identical with those of crystalline, undamaged titanites. At temperatures above 1500 K, the crystal starts to melt and the orientational dependence of the IR absorption is destroyed. The recrystallization processes are quantified and discussed in terms of a percolation behaviour of amorphous and crystalline titanite. It is proposed that hydrogen transport is strongly enhanced during recrystallization.

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“…The crystal structure of pure titanite had been studied previously using classical X-ray diffraction (XRD) [1] and synchrotron radiation [2]. Radiation-induced structural changes occur in the material if radionucleides are present in the structure and decay.…”

Section: Introductionmentioning

confidence: 99%

“…Thermal annealing leads via various steps to a re-established long-range order and to other phenomena like dehydration and volume reduction [3,5,7]. The structural transformation behaviour of synthetic and natural crystalline titanite due to temperature is well known [2,8,9]. * corresponding author; e-mail:…”

Section: Introductionmentioning

confidence: 99%

Local Phenomena in meta-mict Titanite

et al. 2010

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Pure titanite is a mineral with chemical composition CaTiSiO 5 . Its structure consists of corner linked TiO 6 -octahedra, SiO 4 -tetrahedra and sevenfold coordinated Ca positions. In nature various impurities like U and Th can be incorporated in the structure showing alpha and beta radiation. On metamictization, a process which occurs in nature when a mineral is exposed to radioactive irradiation, strong modifications of the structure are observed. Recoil processes due to alpha radiation change over geological time scales the originally periodically structured material into a quasi-amorphous state with persisting short-range order but destroyed long-range order. We report IR and Raman spectra as well as X-ray diffraction data of metamict and heat treated titanite from the Cardiff mine, Canada. IR as well as the Raman modes are strongly broadened in the metamict material and sharpen on annealing. The OH-stretching mode at 3486 cm −1 indicates strong changes in the local environment of OH in metamict titanite. The appearance of the Raman excitations between 620 and 750 cm −1 in metamict titanite, which in IR spectra are due to Ti-O stretching from TiO6 octahedra, indicates the breakdown of the Raman selection rules. This points to the breaking of the octahedral symmetry of TiO6 polyhedra.

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The two-step phase transition of titanite, CaTiSiO5: a synchrotron radiation study

Cited by 45 publications

References 16 publications

Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase

Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase

Dehydration and recrystallization of radiation-damaged titanite under thermal annealing

Local Phenomena in meta-mict Titanite

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