Fast mapping of inhomogeneities in the popular metallic perovskite Nb:SrTiO₃by confocal Raman microscopy

Abstract

Confocal Raman microscopy was applied in order to investigate the homogeneity of donor doping in Nb:SrTiO3 single crystals. Measurements of local Raman spectra revealed a systematic relation between the intensity of the Raman signal and the donor content of the crystals. We successfully elaborated a correspondence between the electronic structure and the intensity of the Raman lines using a crystal with macroscopic inhomogeneity as a demonstration sample. By mapping the distribution of the intensity of the Raman signal, we identified a characteristic inhomogeneous structure related to the presence of clusters with sizes of 5 µm to 20 µm, indicating inhomogeneous donor distribution caused by flaws introduced during crystal growth. Hence, we propose confocal Raman microscopy as a convenient technique for investigating the homogeneity and quality of doped perovskite surfaces, which are needed for various technological applications. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Homogeneity and variation of donor doping in Verneuil-grown SrTiO3:Nb single crystals

“…As described in our earlier work 24 , imperfections of Verneuil-grown crystals can already be seen in some samples with the naked eye when cutting the crystal boule in slices with thicknesses below 0.5 mm. In Fig.…”

“…The modulation signature of these variations appears to be production dependent indicating tiny imperfections of the crystal growth process as their origin. In addition, spatial inhomogeneities of further optical phenomena such as the intensity of the Raman effect and the lifetime of the fluorescence have been found on crystals with comparable quality 24 25 but they do not directly imply that an inhomogeneous Nb distribution is present in the crystal as discussed below. On the other hand, it is possible to purchase Verneuil grown Nb-doped (1 at%) single crystals of even higher quality from a different supplier in which these modulations of the optical transmissivity are below the detection limit ( Fig.…”

“…But since the Verneuil growth takes place far away from the thermodynamic equilibrium, a deviation from a statistical distribution cannot be excluded theoretically. In fact, we recently investigated the optical properties of Nb-doped SrTiO 3 single crystals qualitatively using optical microscopy, confocal Raman microscopy, and fluorescence lifetime imaging microscopy revealing an inhomogeneous structure of the distribution of Ti 3+ states on the microscale 24 in randomly selected regions of several commercial crystals 25 . Furthermore, we found conductive clusters in the range of few tens of nanometres on the surface when we used local conductivity atomic force microscopy to perform redox-based resistive switching and it was speculated that these clusters may originate from inhomogeneous Nb distributions 26 .…”

Structural characterisation of slightly Fe-doped SrTiO3 grown via a sol–gel hydrothermal synthesis

“…4a. By comparing these Raman spectra with the published data [24,[33][34][35][36][37][38][39], three firstorder phonon modes were identified at approximately 171, 540 and 800 cm -1 corresponding to the TO 2 , TO 4 and LO 4 modes, respectively. The frequencies of the TO 2 and TO 4 / LO 4 modes have been determined by fitting with Fano and Lorentzian line shapes, respectively.…”

Influence of mechanical activation on SrTiO3 mixture with Fe2O3 as aditive

“…Inkorporacija Fe 4+ jona narušava inverzionu simetriju što dovodi do pojave aktivnih Raman moda [31][32][33] dok prisustvo kiseonikovih vakancija narušava strukturu oktaedra što rezultira pojavom Raman moda prvog reda. Raman spektri STOFe snimljeni na sobnoj temperaturi (Slika 4) su upoređeni sa ranije dobijenim Raman spektrima [27,28,[34][35][36][37][38][39] i primećena je pojava Raman modova prvog reda ~ 83, 118, 179, 535 i 868 cm -1 identifikovanih kao TO1, LO1, TO2, TO4 i LO4, istim redom.…”