1. Synthesis and Characterization of Li2TiSiO5 Obtained by Melting and Solid-State Reaction
Franciele R. CESCONETO1, Sabrina ARCARO1, Marcelo T. SOUZA1, Alexandre H. B. TEIXEIRA1, Fabiano RAUPP-PEREIRA1, Oscar R. K. MONTEDO2, Antônio P. NOVAES DE OLIVEIRA1
Graduate Program in Materials Science and Engineering (PGMAT/PPGCEM)
1Laboratory of Glass-Ceramic Materials (VITROCER) - Federal University of Santa Catarina (UFSC)
2Laboratory of Technical Ceramics (CERTEC) - Catarinense Extreme South University (UNESC)
INTRODUCTION
RESULTS AND DISCUSSION
It can be seen by examination of Figure 1a in the heating curve, the first exothermic event (E1) between 600 and 700 °C which is related to the crystallization of Li2TiO3 compound. Among 840 and 985 °C it can be observed a second exothermic event (E2) concerning the crystallization of Li2TiSiO5 compound and, at approximately 1200 °C, an endothermic event (E3) which is related to melting. In the cooling curve, in Figure 1a, it can be seen just one exothermic event (E2') quite intense in the same temperature range as the E2 event, indicating the crystallization of Li2TiSiO5.
Semiconductor materials that present generic formula type A2TiOBO4 (A = Li, Na and B = Si, Ge) present photoluminescence. Such titanates, have distorted octahedra TiO6 with a short Ti-O bond distance that, in isolation, provide efficient room temperature photoluminescence.
The photoluminescence is important in many scientific and technological fields, with important applications, especially those based on fluorescence, as the investigation of properties of matter, detection and analysis, visualization (fluorescence microscopy), diagnosis, fluorescent lamps and tubes, optical brighteners, screens plasma, in hydrogeological markers, fluorescent and phosphorescent inks, safety signs, detection of counterfeit documents, among others.
The luminescence light emission is a phenomenon manifested by forms of cold body radiation without increasing the temperature, otherwise the incadescence. There are several types of luminescence, which differ by the energy used for excitation, among these is the photoluminescence, an optical phenomenon produced when a material is excited by electromagnetic radiation and exhibits an emission in the form of photons (electromagnetic radiation). This emission that is related to the structural disorder (atomic and/or molecular) induces the formation of different energy states in the gap between the valence band and the conduction band, facilitating the transition of electrons. Thus the photoinduced properties are determined by the level of interaction between electromagnetic radiation and electrons of the atoms of the material.
Compounds A=(Li2TiBO5) are highly luminescent when excited with electromagnetic radiation of 250 nm wavelength. The lithium titanossilicate (Li2TiSiO5) is part of this group of compounds presenting photoluminescence at room temperature with excitation at 488 nm, unlike other compounds in this class. In the phase diagram of the SiO2-TiO2-Li2O system, it can be seen that the compound Li2TiSiO5 melts in 1213 ± 8 °C. Some attempts to synthesize this compound are found in the literature, such as by co-hydrolysis, the polymeric precursors, a mixture of oxides, with all these forms of processing consumes much time and energy.
Therefore, this work reports results of the synthesis of Li2TiSiO5 from two distinct routes: (i) melting a stoichiometric mixture of Li2CO3, TiO2 (nanoparticulate) and SiO2 and (ii) solid state reaction from a mixture of TiO2 (nanoparticulate) and Li2SiO3 (obtained by melting).
Figure 1. Curves of differential thermal analysis (DTA) of (a) LTS(i) and (b) LS(f) and LTS(ii).
In Figure 1b, you can not observe events exothermic evident for both LS(f) and LTS(ii) curves. However, it is possible to identify an endothermic event E3(i) and E3(ii) at approximately 1200 °C related to melting.
From Figure 2a, it can be seen the main crystalline phases attributed to the lithium titanossilicato, Li2TiSiO5 (α) and lithium titanate, Li2TiO3 (β). For the samples treated at 900 °C, the disappearance is observed in the Li2TiO3 at 43º (relative to compound LTS(i) without heat treatment) in contrast to the intensification of the peaks relating to Li2TiSiO5 (α) at 20, 24, 28 and 34º.
EXPERIMENTAL
ROUTE(i)
ROUTE(ii)
Mixture of Raw Materials
(Li2CO3, SiO2, TiO2 (nanoparticulate))
(Li2CO3, SiO2)
Melting
(1550 °C/2 h)
Milling
(30 min)
Drying
(110 °C/2 h)
Thermal Treatment
( °C/1 h)
Characterization
DTA
XRD
TiO2 (nanoparticulate)
Figure 2. X-ray diffractograms of (a) LTS(i) and (b) LTS(ii), both thermally treated at 900, 950 and 1000 °C/1 h. α = Li2TiSiO5; β = Li2TiO3; λ = Li2SiO3; ψ = TiO2.
In Figure 2b, the main crystalline phases were attributed to lithium metasilicate, Li2SiO3 (λ), lithium titanossilicato, Li2TiSiO5 (α) and rutile TiO2 (ψ). In the diffractogram relating to LTS(ii) compound without thermal treatment (Figure 2b) it was observed only peaks related to Li2SiO3 crystalline phase (λ). In the samples thermally treated at 900 °C occurs the appearance of peaks related to Li2TiSiO5 at 20, 24, 27, 34, 41 and 47º and rutile at 36º. With the temperature increased to 1000 °C it is observed an increase of the intensity of the diffraction peaks relating to the main phase Li2TiSiO5.
CONCLUSIONS
Li2SiTiO5 (i)
LTS(i)
Li2SiTiO5 (ii)
LTS(ii)
Comparing the synthetic routes, it is clear that the synthesis route by melting, route(i), allowed (after heat treatment) to obtain, mainly, the compound of interest in this work, Li2TiSiO5, with little variation over 950 °C, while the route synthesis of precursors for reaction in the solid state, route(ii), resulted in the formation of Li2TiSiO5 and other different crystalline phases after the heat treatment.
CerTec
*Contatc:
Acknowledgmentes: CNPq and CAPES