Titanite CaTiSiOs

Titanite (formerly called sphene ) is an orthosihcate mineral with the chemical formula CaTi0Si04, where approximately 20% of the oxygens can be partially replaced by OH (hydroxyl) and F. Titanite has a monochnic symmetry 

The natural titanite in our study consisted of nine samples. Concentrations of potential luminescence impurities in one sample are presented in Table 4.12. The laser-induced time-resolved technique enables us to detect Sm +, Nd, Tm , Pr , Er , Eu and Cr emission centers (Figs. 4.33-4.34). 

a-f Laser-induced time-resolved luminescence spectra of titanite demonstrating Cr , Nd , Tm and possibly Ti centers 

Benitoite is a rare, strongly dichroic, blue mineral used as a gemstone. In spite of much effort in its study, the origin of color in benitoite has not been definitively estabhshed. Because traces of Fe are found, ideas proposed include the Fe -Ti or the Fe -Fe inter-valance charge transfer. While most benitoite is colorless when viewed down the c-axis, there are a very small number of exceedingly rare stones, which are pink in this direction (Rossman 1988). 

Benitoite is characterized by very intensive blue luminescence (White 1990). Laser-induced time-resolved technique enables us to detect three broad bands and one narrow line, connectet with TiOe, Ti and Cr or Mn, luminescence centers (Fig. 4.35). 

Titanite (formerly called sphene ) is an orthosilicate mineral with the chemical formula CaTi0Si04, where approximately 20 % of the oxygens can be partially replaced by OH (hydroxyl) and F. Titanite has a monoclinic symmetry with a space group P2i a. It has optically positive character with a= 1.84—1.95, P= 1.87—2.034, 7 = 1.943—2.11, very high refractive indices (1.843-1.950) and extreme birefringence (0.100-0.192). The structure of titanite consists of chains of octahedral sites occupied by Ti , cross-linked by isolated Si04 tetrahedra. Large 

Excitation by CW laser with 514 nm revealed several IR luminescence (Fig. 4.81). They may be evidently ascribed to Nd emission. Many luminescence lines in the IR part of the spectrum have been found under excitation with 785 nm 

Detailed research of titanite REE luminescence under different cw laser excitations was done by Lenz et al. (2015) including the study of luminescence and its excitation of artificial titanite samples activated by different REE, such as Sm, Nd, Pr and Eu. Relative emission intensities of individual REEs depend strongly on the excitation wavelength. The Raman spectra of titanite obtained using a 473 nm laser excitation shows emissions of Pr, Sm and Nd , whereas green excitation (532 nm) excites preferentially the PL of Sm , and Nd , red excitation (633 nm) predominantly Cr and Nd , and NIR excitation (785 run) Nd only. Those results have been confirmed by excitation spectroscopy of artificially activated titanite samples. Under 785 mn excitation, Nd emissions are exceptionally strong (whereas Raman scattering is weaker under NIR excitation when compared to visible excitatirui). Therefore, Raman spectra of titanite samples obtained with IR excitation typically are obscured vastly by Nd emissions. 

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Titanite CaTiSiOs West Africa, Australia aircraft, missiles... 

Figure 10. Projection of the structure of titanite (CaTiSiOs) on the (001) plane. Ti cations within octahedral chains parallel to a are interconnected via silica tetia-hedra. Spheres are Ca cations.

Titanite (CaTiSiOs) is an excellent example of a mineral in which small amounts of impurities will precipitate high densities of antiphase boundaries. Titanite contains parallel kinked chains of TiOe octahedra that are interconnected by Si04 tetrahedra, with Ca cations in irregular 7-coordination (Fig. 10). At room temperature, the Ti cations are... 

Tarascon JM, Greene LH, McKirmon WR, Htrll GW, Geballe TH (1987) Superconductivity at 40 K in the oxygen-defect perovskites La2 cSr Cu04 y. Science 235 1373-1376 Taylor M, Brown GE (1976) High-temperatrrre structrrral study of the P2 /a-A2/a phase transition in synthetic titanite, CaTiSiOs. Am Mineral 61 435-447... 

In this work we focus on the short range order in ferroelastic lead phosphate, Pb3(P04)2, in Sr-doped lead phosphate crystals, in antiferroelectric titanite, CaTiSiOs, and isosymmetric effects in malayaite, CaSnSiOs. 

Synthetic titanite, CaTiSiOs, undergoes structural phase transitions near 500 K and ca. 825 K (Salje et al. 1993 Zhang et al. 1996 Kek et al. 1997 Malcherek et al. 1999a). The phases were described by Chrosch et al. (1997) as a for the room-temperature... 

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Etude par diffusion inelastique des neutrons. J Phys 40 1185-1194 Kek S, Aroyo M, Bismayer U, Schmidt C, Eichhom K, Krane HG (1997) Synchrotron radiation study of the crystal structure of titanite (CaTiSiOs) at lOOK, 295K and 530K Model for a two-step stractrual trarrsitioa Z Kristallogr 212 9-19... 

Salje EKH, Graeme-Barber A, Carpenter, MA, Bismayer U (1993) Lattice parameters, spontaneous strain and phase transitions in Pb3(P04)2. Acta Ciystallogr B49 387-392 Salje EKH, Schmidt C, Bismayer U (1993) Structural phase transition in titanite, CaTiSiOs A Ramanspectroscopic study. Phys Chem Miner 19 502-506 Speer JA, Gibbs GV (1976) Crystal structure of synthetic titanite CaTiSiOs, and the domain textures of natural titanites. Am Mineral 61 238-247... 

Van Heurck C, Van Tendeloo G, Ghose S, Amehnckx S (1991) Paraelectric-antiferroelectric phase transition in titanite, CaTiSiOs. II. Electron diffraction and electron microscopic studies of transition dynamics. Phys Chem Miner 17 604-610... 

Yagil Y, Baundenbacher F, Zhang M, Birch JR, Kinder H, Salje EKH (1995) Optical properties of YiBa2Cu307-6 thin films. Phys Rev B 52 15582-15591 Zhang M, Salje EKH, Bismayer U, Unruh HG, Wruck B, Schmidt C (1995) Phase transition(s) in titanite CaTiSiOs an infrared spectrosopic, dielectric response and heat capacity study. Phys Chem Miner 22 41-49... 

Titanite A calcium titanium silicate mineral with the formula CaTiSiOs Sometimes called sphene. 

Pure primary titanium dioxide does not occur naturally, but is derived by weathering from ilmenite (FeTiOs), perovskite (CaTiOs), and titanite (sphene) (CaTiSiO ). The weathering products form leuxocene ores with up to 68% mtile content. The... 

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