Lithium Borophosphate Glasses Research Articles

EPR, optical absorption and photoluminescence properties of Cr 3+ ions in lithium borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence studies of Cr 3+ ions in lithium borophosphate glasses have been studied. The EPR spectra exhibit two resonance signals with effective g values at g = 4.56 and g = 1.96. These resonance signals are attributed to isolated Cr 3+ ions and exchange coupled Cr 3+ pairs, respectively. The EPR spectra have also been studied at various low temperatures. The population of spin levels ( N) participating at resonance signal g = 1.96 has been calculated as a function of temperature. The spin-population ( N) is found to be increasing with decrease in temperature. The magnetic susceptibility ( χ) was calculated from the EPR data. It is observed that as temperature decreases, χ increases in accordance with Curie–Weiss law. The exchange coupling constant J between Cr 3+ ions is calculated from the relative intensities of g = 1.96 resonance line at various temperatures. The optical absorption spectrum exhibits four bands characteristic of Cr 3+ ions in octahedral symmetry. From the optical absorption spectral data, the crystal field (Dq) and Racah parameters ( B and C) have been evaluated. The luminescence spectrum exhibits a red emission peak, which is assigned to a transition from the upper 4T 2g (F) → 4A 2g (F) ground state of Cr 3+ ions. The optical band gap is evaluated from the ultraviolet absorption edges.

Composition and structure dependence of the properties of lithium borophosphate glasses showing boron anomaly

This work presents a study on the structure, microstructure and properties of 50Li 2O· xB 2O 3·(50 − x)P 2O 5 glasses. The structure has been studied through NMR spectroscopy and the microstructure by TEM. The properties of the glasses are discussed according to their structure and microstructural features. The introduction of boron produces new linkages between phosphate chains through P–O–B bonds, whose amount increases with boron incorporation; at the same time, a depolymerisation of the phosphate chains into Q 1-type phosphate units takes place. The introduction of boron produces an increase in T g together with a decrease in the molar volume. The room temperature electrical conductivity increases with boron content as well. However, B 2O 3 contents higher than 20 mol% lead to crystallisation of lithium orthophosphate which contributed to hinder ionic conduction of the glasses.

Modification of network structure induced by glass former composition and its correlation to the conductivity in lithium borophosphate glass for solid state electrolyte

The xLi 2O–(1 − x)( yB 2O 3–(1 − y)P 2O 5) glasses system is one of the parent compositions for chemically and electrochemically stable solid state electrolyte applicable to thin film battery. The purpose of this study was to seek an optimum composition maximizing the ionic conductivity for the deposition of thin film electrolytes. xLi 2O–(1 − x)( yB 2O 3–(1 − y)P 2O 5) glasses were prepared with wide range of composition, i.e. x = 0.40–0.47 and B 2O 3/(B 2O 3 + P 2O 5) ratio was 0.17–0.67 ( y = xx ∼ xx). The structural variation of the oxide Li 2O–B 2O 3–P 2O 5 system was investigated by Raman spectroscopy to find out the correlation with the electrical conductivity. It was shown that under 40 mol% of Li 2O the ionic conductivity monotonically increased with increasing of B 2O 3, while over the 40 mol% of Li 2O it exhibited a maximum at a specific B 2O 3/(B 2O 3 + P 2O 5) ratio, typically ∼ 0.5. The structural investigation indicated that the variation in conductivity was closely correlated to the variation of 4-coordinated boron groups.

Conductivity of Lithium Borophosphate Glasses for Thin Film Solid Electrolyte of Lithium Battery

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The optical and 57Fe Mössbauer spectra of lithium diborate (Li 2B 4O 7) in borophosphate glass-ceramics

In this paper lithium borophosphate glasses and glass-ceramics in the system 66.6| xB 2O 3·(100− x)P 2O 5|. 33.3Li 2O: yFe 2O 3 with 0⩽ x⩽100 mol% and y=4 mol%, were studied by X-ray powder diffraction, 57Fe Mössbauer and infrared spectroscopy. All the samples in the system present a glass or glass-ceramics behavior which is confirmed by X-ray diffraction. The substitution of P 5+ by B 3+ associated with the increase of the ratio B 2O 3/P 2O 5 leads to oxidation of the iron in the samples which was detected by Mössbauer spectroscopy. From our Mössbauer analysis, high-spin Fe 2+ and Fe 3+ in a distorted octahedral coordination are present in all samples. For heat-treated samples we have the precipitation of crystalline phase of Li 2B 4O 7 and for others lithium borate phases which was confirmed by X-ray powder diffraction. The Mössbauer spectra for some heat-treated samples show, besides the paramagnetic doublets, a magnetic sextet component with hyperfine magnetic field ( B hf=50 T). These magnetic phases were not identified up to this point in our study but we believe that these parameters are quite close to Hematite (α-Fe 2O 3). The boric acid phase H 3BO 3 were also identified by the X-ray diffraction, and infrared spectroscopy for x=26.6, 40 and 53.3 mol%. Such glasses and glass-ceramics containing nonlinear optical materials formed in a controlled crystallization process would be interesting candidates for application in new electro-optic devices.

Structural studies of lithium triborate (LBO–LiB3O5) in borophosphate glass-ceramics

In this paper lithium borophosphate glasses and glass-ceramics in the system 0.75|xB2O3.(100−x)P2O5|.25Li2O.yFe2O3 with 0≤x≤100 mol.% and y=4 mol.%, were studied by X-ray powder diffraction, Mössbauer and infrared spectroscopy. All the samples in the system present a glass or glass-ceramic behavior which was confirmed by X-ray diffraction. From our Mössbauer analysis, high spin Fe2+ and Fe3+ in a distorted octahedral coordination are present in all samples. One can conclude that both iron ions are at sites of distorted octahedral coordination, acting as network modifiers (NWM) in a very broad site distribution, which is characteristic of an amorphous structural neighborhood. Such glasses and glass-ceramics containing nonlinear optical materials formed in a controlled crystallization process would be interesting candidates for applications in new nonlinear optical devices.

NMR studies of lithium borophosphate glasses

The lithium borophosphate glasses were studied by 11B and 31P nuclear magnetic resonance spectroscopy. It was found that the fractions of BO 4 units present are greater than 0.5 and this result implies that there are boron phosphate units in the glasses. The boron phosphate unit, whose structure is different from that of BPO 4, consists of one PO 4 unit, in which there is a P=O bond, and one BO 4 unit. The two tetrahedral units are linked by a shared oxygen atom. The excess of negative charge is distributed over the phosphate and borate units and is compensated by a cation. The majority of the glasses studied mainly consist of boron phosphate units. The fractions of BO 4 units vary with the different compositions of the glasses.

Raman studies of lithium borophosphate glasses

In the past few years, studies of the changes in Raman spectra and ionic conductivity in some glasses in silicate, borate and phosphate systems showed that the ionic conductivity of the glass was mainly dependent on the total number of active ions Li + or Na +, but there was also an effect of the glass structure on conductivity. When Al 3+ and/or B 3+ ions were present in the glass in the form of AlO 4 and BO 4 and the excess negative charge on them was compensated by the active cation ion, the glass would have higher ionic conductivity. A detailed investigation of the Raman spectra of Li 2OB 2O 3P 2O 5 glasses has shown that besides phosphate groups, such as metaphosphate (PO 3) n n− , tetraphosphate (P 4O 13) 6−, triphosphate (P 3O 10) 5− and pyrophosphate (P 2O 7) 4−,a nd borate groups, such as diborate (B 4O 7) 2− and chain-type metaborate (BO 2) −, there may also be different of kinds of phosphate groups containing BO 4 units, (BOP) 0 and (BOP) −, groups present in this glass system. The active ability of Li + ions present in (B 4O 7) 2–, phosphate groups with BO 4 units and BO 4 units and (BOP) − groups is higher than those present in various phosphate groups with non-bridging oxygen(s).

Enhancement of the ionic conductivity of lithium borophosphate glass: a mixed glass former approach

The electrical conductivity of the lithium borophosphate system has been studied. An enhancement in the ionic conductivity has been obtained via the mixed glass former effect. Two maxima have been observed in the conductivity and have been explained by using a thermodynamic approach. The highest conductivity at 30 °C is 1 × 10 −6 (ohm cm) −1, corresponding to a Li/P ratio of unity. Glass with this composition may find useful application in electrochemical power sources.