Second order Raman spectrum of rutile TiO₂

Abstract

Data are presented on the second order Raman spectrum of rutile TiOt for various scattering geometries, at room and liquid Nz temperatures. The results of a standard critical point analysis (i) allow the most important addition processes at low energies to be identified, (ii) indicate the importance of matrix element effects, and (iii) cannot account for a peak at 172 cm-' for the Y ( x y ) X geometry.The Raman and infrared fundamental modes of rutile at the r point of the Brillouin zone have been assigned in many papers published previously' and extensive neutron scattering data are available for the r, X , M and 2 points' with symmetry assignment. To our knowledge, however, no one has assigned the second order Raman spectra of this crystal, which are very intense. In this work we present data on and a preliminary analysis of the second order Raman scattering in rutile TiOz.The sample was purchased from MRC and it was grown by the Verneuil technique, all impurities were stated to be less than 100 ppm, and the possible effects of vacancies were minimized by oxidizing the crystal in a furnace for several hours. The crystal was oriented by X-rays, cut and polished, and mounted in a liquid nitrogen cryostat described elsewhere.' The data were taken with a conventional Raman scattering system, using an Ar laser operating at 4880 A with a power of about 400 mW. A pair of Glan polarizers with extinction ratio of 1 : 1@ were used as a laser polarizer and scattering light analyzer in order to eliminate 'leak through' of signals in the wrong polarization. The double spectrometer was set on a resolution better than 0.8 cm-' and a typical counting rate of 10' countss-' was achieved in the region of 250 cm-' of the spectrum. In Fig. 1 are shown the room temperature spectra in the region of 250 cm-' whereas Fig. 2 shows the region of the spectra most important for multi-phonon study. The latter spectra were taken at liquid nitrogen temperature.Our aim is to provide a preliminary analysis of the second order Raman spectra of rutile Ti02 presented above. Thus we limit ourselves to a consideration of the overtone and combination two-phonon processes taking into account only the special points r, X , M and Z of the Brillouin zone.Rutile TiOz has the space group Dtt with two molecules, i.e. six ions per primitive cell. This means that we have a very large number of phonons (18 per Brillouin zone point). The lattice dynamics have been studied both by the rigid ion and shell model appro ache^.'.^ The latter, not surprisingly, yields better fits to the neutron data. In ' Table 1 we show the relevant phonon symmetries and energies. To study the two-phonon processes we perfoim the standard group-theoretical calculations, obtaining the irreducible representations of the full space group 0:; at the special points I', X , M and Z? The Kronecker products (combinations) or symmetrized Kronecker products (overtones) of these 300 200 I00 cm-1 Figure 1. Raman room temperature spectrum of Ti02 near the strong two phonon region: (a) x y componen...

Spectral decomposition of Raman spectra of mixed‐phase TiO2 thin films on Si and silicate substrates

“…Rutile and brookite are present in our films to only a small degree (<20%), and their models are simplified as compared with anatase. The rutile background model was derived the same way as shown for anatase and agrees well with a study of Nicola et al [51] In the fitting routine, the widths of the bands are kept constant. The model for the complex phase brookite is more simplified: in the fitting routine, the brookite background spectrum of Figure S4 is added to the total modeled spectrum with a linear factor.…”

Effect of etching on the composition and structure of anodic spark deposition films on titanium

“…To meet this aim, the samples were fully characterized using Raman spectroscopy. From the Raman spectrum of TiO 2 many different information can be obtained: titanium oxide phase fraction [22,23], crystallinity, crystallite size [24] and residual stresses [25] down to a minimum coating thickness of about 100 to 250 nm, depending on the substrate chemistry [26]. Crystallographic alterations caused by small amounts of dopants into the TiO 2 structure can also be easily discriminated by the appearance of their associated Raman bands [27], thus making Raman spectroscopy adequate for the characterization of functionalized titanium oxide layers [28][29][30].…”

Influence of Zr dopant on polarization in rutile (In0.5Nb0.5)0.005(Ti1‐xZrx)0.995O2 ceramics

“…Four Raman peaks reflecting these modes detected in the INZT samples, thus indicated that the rutile structure had indeed been obtained. Moreover, a peak at ~250 cm −1 which is ascribed to the second‐order Raman scattering in the rutile structure, was clearly observed . B 1g and A 1g are respectively associated with the O–Ti–O bond bending and Ti–O stretching modes, respectively.…”

“…Moreover, a peak at ~250 cm −1 which is ascribed to the second-order Raman scattering in the rutile structure, was clearly observed. 36 B 1g and A 1g are respectively associated with the O-Ti-O bond bending and Ti-O stretching modes, respectively. The E g mode is attributed to the liberation of out-of-phase oxygen atoms along the c-axis.…”