Raman Spectroscopic Investigations of Dicalcium Silicate: Polymorphs and High‐Temperature Phase Transformations

Abstract

Polymorphs and high-temperature phase transformations␣Ј L -Ca 2 SiO 4 (with ␣Ј L generally considered as a superstructure referring to the ␣Ј H lattice) 3,4,10,11 and ␣-Ca 2 SiO 4 , structurally of dicalcium silicate (Ca 2 SiO 4 ) are investigated on powdered samples, using Raman scattering techniques. Raman specstill uncertain with trigonal 12,13 or hexagonal symmetry, 14 are stable as pure Ca 2 SiO 4 only at elevated temperatures. The tra at room conditions of pure ␥-and ␤-Ca 2 SiO 4 and stabilized ␤-, ␣ L -, and ␣-Ca 2 SiO 4 are presented in the frequency sequence of phase transformations generally accepted is that in Fig. 1, 15 and the proposed transformation mechanisms are as range of 110-1100 cm ؊1 . Each polymorph can be identified by its Raman spectrum, even though strong similarities follows: a semireconstructive mechanism between ␣ and ␣Ј H ; 14 a second-order transformation 16 or a displacive transformation exist between the ␤, ␣ L , and ␣ phases. In-situ hightemperature Raman spectroscopic studies in the temperamechanism between ␣Ј H and ␣Ј L ; 14 a displacive, 14 possibly martensitic, mechanism 17 or a first-order transformation between ture range of 298-1433 K on heating and cooling also are ␣Ј L and ␤; 16 a reconstructive 14 or a semireconstructive ␥ → reported, starting from ␥-Ca 2 SiO 4 . Modifications occurring ␣Ј L transition; 5 and a reconstructive, 14 semireconstructive, 5 or in the Raman spectra recorded in the wavenumber range of displacive mechanism for the ␤ → ␥ phase transformation. 18,19 90-1000 cm ؊1 show up during heating, the irreversible Besides these five phases, an additional phase intermediate ␥ → ␣ L phase transformation. Coexistence of ␥ and ␣ L between ␥ and ␣Ј L has sometimes been observed. 20-22 grains is observed in the temperature range of 1091-1119 K In most cases, X-ray diffractometry (XRD) and differential at least. The differences observed between the ␥-Ca 2 SiO 4 thermal analysis (DTA) are the techniques used to attempt and ␣ L -Ca 2 SiO 4 Raman spectra suggest that this phase to clarify the polymorphism and phase transformations in transformation is a reconstructive first-order transition.Ca 2 SiO 4 . 4,14,16,21 In this study, application of Raman spectrosThe reversible ␣ L → ← ␤ phase transformation also is copy is described and viewed as a complementary technique to described. Raman spectra of pure ␤ and ␣ L phases resemble the previous ones. Indeed, vibrational spectroscopy is a useful each other. The transition occurs from 949 K, on cooling, to tool for sample characterization and analysis and for the calcu-960-988 K, on heating, with a hysteresis probably depenlation of thermodynamic and elastic properties. Vibrational dent on the thermal history of the starting product. From frequencies also are very sensitive to interatomic forces. Indithe Raman scattering observations, this phase transformavidual peaks may be associated with the presence of particular tion also is considered as a first-order transformation and is structural groups within the sample. Thus, Ram...

Phase transitions in single phase Si–Ca–P-based ceramic under thermal treatment

“…For phosphate compounds, ␤-TCP bands were observed at 370-505, 530-645, and 995-1120 cm −1 , respectively assigned to the 2 , 4 and 3 type internal PO 4 3− modes, while ␣-TCP bands were observed at 954-976, 998-1027 and 1058-1077 cm −1 , which agreed with bibliographic databases [25][26][27].…”

Vibrational spectra of CaGa2O4, Ca2GeO4, CaIn2O4 and CaSnO3 prepared by electrospinning

“…3(b), the intense Raman peaks occur at 662 cm −1 , 736 cm −1 , 759 cm −1 , which are most probably assigned to the stretching vibrations of GeO 4 tetrahedra [23,26,47]. Classically, the Raman and IR modes in the range of 600-1000 cm −1 are assigned to stretching modes of the GeO 4 tetrahedra in the structure [23]. Bending vibrations would be expected at lower frequency, but separating these from vibrations involving cations or lattice modes is difficult because of the occurrence of modes coupling and modes mixing.…”

“…1, which are finely indexed to orthorhombic CaGa 2 O 4 [22], orthorhombic Ca 2 GeO 4 (the same as γ -Ca 2 SiO 4 [23]) [24][25][26], orthorhombic CaIn 2 O 4 [27,28], and an orthorhombic phase CaSnO 3 with perovskite structure [29], respectively. The X-ray examination of these oxides also confirmed the presence of the singlephase for all compounds.…”

Applications of Vibrational Spectroscopy to Geology

“…21,83,153 -158 The Raman spectra of forsterite has been measured from 77 to 2000 K. 110 Highpressure and high-temperature phase transition among the various polymorphs of Ca 2 SiO 4 have been investigated by Raman spectroscopy. 159,160 The thermodynamic and thermoelastic properties of forsterite and fayalite have been calculated over a wide range of pressure and temperature conditions using IR and Raman data. 63,154,158,161 There exist several systematic IR and Raman spectra of garnets in the (Ca,Fe,Mg,Mn) 3 (Al,Fe) 2 Si 3 O 12 (pyrope-grossular-almandine-spessartine) system 162 -170 ( Figure 8).…”