Structure of lanthanum-borogermanate glass with stillwellite composition according to vibrational spectroscopy data

Abstract

Translated from Steklo i Keramika, No. 4, pp. 9 -12, April, 2010. Dielectric IR spectroscopy and Raman scattering (RS) spectroscopy have been used to confirm the presence in the structure of lanthanum-borogermanate (LBG) glass of triply coordinated boron atoms which are absent in a LaBGe 5 crystal. The grouping ratio [BO 3 ]/[BO 4 ] is independent of the conditions under which the glass is obtained. It is proposed that amorphous nanosize regions of two types with approximately the same chemical composition but different structure are present in the glass. Regions of the first kind contain predominately quadruply coordinated boron atoms and are the basis for the formation of nuclei of stillwellite crystals, while regions of the second kind are more disordered, and a large fraction of the boron atoms in them lie at centers of oxygen triangles.Lanthanum-borogermanate glasses with compositions close to that of the ferroelectric LaBGeO 5 with stillwellite structure (LBG glass below) have been the objects of numerous studies for almost twenty years. This is because in these glasses it is possible to separate the LaBGeO 5 phase in the form of nanosize crystals [1], strong surface layers of oriented crystals [2], to obtain a quadratic optical nonlinearity in the transparent glass by means of thermal polarization [3], and to perfect crystalline textures possessing pyroelectric properties [4,5].In the last few years LBG glasses have become one of the most important base objects for the development of new technologies of hybrid optical materials based on controllable local crystallization of glass under the action of focused laser radiation. The laser radiation permits forming in LBG glass masses of closely spaced individual crystals with a practically monodisperse size distribution [6] and quasi-single-crystalline structure with complex geometry [7]. Thus, an entire series of promising polar glass-crystalline dielectrics can be obtained on the basis of LBG glasses with composition close to that of stillwellite. But if numerous experimental data have already been accumulated on glass formation in the LBG system and about the crystallization properties of LBG glasses, the information on their structure in the near and medium range scales is based mainly on ideas concerning the structural similarity of glasses and crystals with close compositions.In the case of exact correspondence between the glass and crystalline phase LaBGeO 5 , considering the ease of separating this phase in them, it is natural to suppose that short-range order in LBG glass is similar to short-range order in the crystal and that they form one and the same structural units [8]. However, data which do not fit into this model have appeared recently. In the crystal LaBGeO 5 coordination number of all boron atoms is 4, while according to the nuclear magnetic resonance (NMR) data [1] about half the boron atoms in LBG glass lie at the centers of triangles. This fact contradicts the principle of crystallochemical similarity, formulated and experimentally conf...

Spectroscopic properties of Sm 3+ -doped lanthanum borogermanate glass

“…2 shows IR spectra of all the glasses of this study. Here the intense bands in the 700-800 cm À 1 region correspond primarily to stretching vibrations of GeO 4 tetrahedra with a small contribution from vibrations of BO 4 tetrahedra [18]. The latter are completely masked in the spectrum by the broadened and intense peak due to GeO 4 .…”

Eu3+‐Activated Borogermanate Scintillating Glass with a High Gd2O3 Content

“…The band centered at 420 cm −1 is assigned to the symmetric stretching of bridging oxygen in a line bisecting the Ge–O–Ge plane in predominately six‐membered rings, whereas the Raman band at 574 cm −1 is associated with a combination of bending vibrations of T–O–T (T = Ge or B) bonds . According to the spectroscopic data of LaBGeO 5 crystal , the intense Raman bands peak at ~802 cm −1 are assigned to the stretching vibrations of [GeO 4 ] tetrahedra with a small contribution of vibrations of [BO 4 ] tetrahedra, the latter in the spectrum of the glass is completely masked by the broadened intense peak due to [GeO 4 ] . It seems likely that the bands observed in the frequency range 944 cm −1 can be associated with the presence of isolated orthoborate units (BO 3 ) 3− with three NBOs, which can compensate positive charges of trivalent rare‐earth ions, resulting in high concentrated rare‐earth glass.…”

“…. Besides for the typical absorption band of OH − group at ~3500 cm −1 , the strong absorption at ~735 cm −1 is ascribed to the bending and stretching vibrations of T–O–T (T = B, Ge) linkages, while the high‐frequency region of IR spectra centered at 1160 cm −1 correspond to the vibrations of [BO 3 ] triangle group . However, the similar shape of normalized IR spectra cannot give the evolution of glass structure in detail, Raman spectra are carried out and discussed in the next paragraph.…”

“…28,30 According to the spectroscopic data of LaBGeO 5 crystal , the intense Raman bands peak at~802 cm À1 are assigned to the stretching vibrations of [GeO 4 ] tetrahedra with a small contribution of vibrations of [BO 4 ] tetrahedra, the latter in the spectrum of the glass is completely masked by the broadened intense peak due to [GeO 4 ]. 27 It seems likely that the bands observed in the frequency range 944 cm À1 can be associated with the presence of isolated orthoborate units (BO 3 ) 3À with three NBOs, 31 which can compensate positive charges of trivalent rare-earth ions, resulting in high concentrated rare-earth glass. While band at 1350 cm À1 should be assigned to the B-O À bonds vibration occurring in a large borate network and not to a specific group.…”

Investigation of Luminescence Properties of Tb3+ Ions In Gadolinium Borogermanate Glasses For Green Laser Application

“…İlk bölge 400-800 cm -1 arasında olan bölgedir ve bu bölgede B-O-B ve Ge-O-Ge bağlarının eğilme ve gerilme titreşimleri bulunmaktadır (Sundari et al, 2010;Zhang et al, 2012a). 800-1200 cm -1 arasında yer alan ikinci bölgede yaklaşık olarak 1010 cm -1 deki titreşimler BO 4 biriminin B-O bağ gerilmesinden kaynaklanmaktadır (Sigaev et al, 2010). Son olarak üçüncü bölge 1200-1600 cm -1 merkezlenmiştir ve burada bulunan yaklaşık olarak 1384 cm -1 titreşimleri BO 3 üçlü biriminin B-O bağ gerilmesinin asimetrik gerilme rahatlamasından kaynaklanmaktadır (Sundari et al, 2010).…”