Li2O ZnO Research Articles

Optical Properties and Activation Energy of A Novel System of Cdte Nanoparticles Embedded in Phosphate Glass Matrix

We report growth and optical properties of a novel system of CdTe nanoparticls doped P2O5–Na2O–ZnO– Li2O glass matrix. We have investigated the effect of concentration, annealing time and temperature on the band gap and size of the CdTe semiconductor nanoparticles. In addition the effect of adding ZnO to the glass matrix on the growing of the nanoparticles has been investigated. We found that the addition of ZnO to the glass composition is strongly affecting the growth of the nanoparticles. On the other hand, we have calcu-lated the size polydispersity index which showed narrow size distribution for the prepared nanoparticles. Furthermore, we have estimated the activation energy of diffusion for the prepared CdTe nanoparticles which gave the activation energy with low value~ 44 kJ mol-1.

Spectroscopy and crystal-field analysis of Cr 4+-doped transparent silicate glass-ceramics

We report transparent Cr 4+-doped SiO 2–Al 2O 3–ZnO–Li 2O–K 2O glass-ceramics with broadband infrared luminescence. After heart-treatment, Li 2ZnSiO 4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. Racah parameters of Cr 4+–Li 2ZnSiO 4 glass-ceramics have been calculated, and it was confirmed from absorption spectra that the energy levels of Cr 4+-doped glass-ceramics are close to the cross point 1E and 3T states. No infrared emission was detected in the as-made glass samples, but the broadband infrared emission centered at 1210 nm with the full width at half maximum (FWHM) of more than 250 nm was observed by exciting the glass-ceramics with excitation of an 808 nm laser diode. In order to analyze the located crystal field of Cr 4+ ions, the emission spectra are fitted by multi-peak Gauss fitting. It is seen that the fluorescence spectra are fitted into two Gaussian bands at around 1195 and 1263 nm with band widths of 208 and 278 nm, respectively. The two Gaussian bands at around 1195 and 1263 nm have about the same decay rate, and hence they would probably originate from the same luminescent centers. The observed infrared emission could be attributed to Cr 4+ ions at low-field sites in Li 2ZnSiO 4 glass-ceramics.

Structural and dielectric properties of Li2O–ZnO–BaO–B2O3–CuO glasses

Glass samples of the system (15Li2O–30ZnO–10BaO–(45 − x)B2O3–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant eφ, loss tan δ, a.c. conductivity, σac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration. The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content indicates structural changes of the glass matrix. The glass transition temperature, Tg, and crystallization temperature, Tc, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter (Tc − Tg) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BO3, BO4, and ZnO4. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction.

A low-firing microwave dielectric material in Li 2O–ZnO–Nb 2O 5 system

LiZnNbO 4 ceramic was fabricated by the conventional solid state reaction method and its microwave dielectric properties were reported for the first time. The phase structure, microstructure, and sintering behavior were also investigated. The LiZnNbO 4 ceramic could be well densified at around 950 °C and demonstrated high performance microwave dielectric properties with a low relative permittivity ~ 14.6, a high quality factor (resonant frequency/dielectric loss) ~ 47, 200 GHz (at 8.7 GHz), and a negative temperature coefficient of resonant frequency approzmiately −64.5 ppm/°C. The LiZnNbO 4 ceramic is chemically compatible with Ag electrode material at its sintering temperature. It can be a promising microwave dielectric material for low-temperature co-fired ceramic technology.

ChemInform Abstract: LiZnNb4O11.5: A Novel Oxygen Deficient Compound in the Nb‐Rich Part of the Li2O—ZnO—Nb2O5 System.

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Silver Co‐Firable ZnTiNb2O8 Microwave Dielectric Ceramics with Li2O–ZnO–B2O3 Glass Additive

The effects of Li2O–ZnO–B2O3 glass additive on the sintering behavior, phase formation, microstructure, and microwave dielectric properties of ZnTiNb2O8 ceramics have been investigated. The sintering temperature of ZnTiNb2O8 ceramics can be effectively reduced from 1200°C to 875°C by adding a small amount of Li2O–ZnO–B2O3 glass, while no obvious degradation of the microwave dielectric properties was induced. Typically, the 2.0 wt% Li2O–ZnO–B2O3 glass‐added ceramic sintered at 875°C has better microwave dielectric properties of ɛr=31.8, Q×f=25,013 GHz, and τf=−62 ppm/°C. In addition, the ceramics can be co‐fired well with an Ag electrode.

Electrical behaviour of Li 2O–ZnO–SiO 2 glass and glass-ceramics system

Sealing quality lithium zinc silicate (LZS) glasses of compositions (wt.%) (a) LZSL– Li 2O: 12.65, ZnO: 1.85, SiO 2: 74.4, Al 2O 3: 3.8, K 2O: 2.95, P 2O 5: 3.15, B 2O 3: 1.2 (low ZnO), and (b) LZSH– Li 2O: 8.9, ZnO: 24.03, SiO 2: 53.7, Na 2O: 5.42, P 2O 5: 2.95, B 2O 3: 5 (high ZnO) were prepared by conventional melt-quench technique and converted to glass-ceramics by controlled crystallization process. The electrical properties of these samples were measured using ac impedance spectroscopy technique over a frequency range of 10 Hz–15 MHz at several temperatures in the range of 323–673 K. The ac conductivity, dc conductivity, dielectric constant and loss factor were obtained from these measurements. The dc conductivity ( σ dc) follows the Arrhenius behaviour with temperature. It is observed that σ dc in LZSL glass is significantly higher than in the LSZH glass and the activation energies for σ dc for LZSL and LZSH glasses are 0.59 and 1.08 eV, respectively. It further observed that the conductivity value decreases nearly one order of magnitude on conversion to glass-ceramics. The behaviour is explained on the basis of distributions and nature of alkali ions and network structures in these samples.

Structural and electrical properties of Li 2O–ZnO–P 2O 5 glasses

Lithium zinc phosphate glasses of the composition xLi 2O–(40 − x)ZnO–60P 2O 5, (0 < x < 40), in mol%, were prepared by melting and analyzed by different thermal analysis (DTA), Raman and impedance spectroscopy in the frequency range from 0.01 Hz to 4 MHz and temperature range from 303 to 473 K. The systematic change in the variety of properties at 20 mol% Li 2O is explained by changes in the nature of the oxygen bonds in glass network. The Raman spectra predominantly show the metaphosphate structure with barely detectable pyrophosphate units for all glasses in the series. However, replacing ZnO with Li 2O in these glasses leads to the compositional dependent changes. This dependence is explained by different structural cross-linking of phosphate chains with increasing Li 2O, which is correlated with the unusual T g minimum at 20 mol% Li 2O. The electrical conductivity as a function of Li 2O concentration measured at lower temperatures (298 and 363 K) passes through a minimum at 20 mol% whereas linearly increases at higher temperatures. This suggests that the conductivity enhancement is directly related to the thermally stimulated mobility of Li + ions in the high temperature region. The observed minimum in electrical conductivity at 20 mol% Li 2O is due to the structural reorganization of the glass network. With increasing Li 2O content up to 40 mol% the values of electrical conductivity increases for five orders of magnitude indicating ionic conductivity.

LiZnNb 4O 11.5: A novel oxygen deficient compound in the Nb-rich part of the Li 2O–ZnO–Nb 2O 5 system

A novel lithium zinc niobium oxide LiZnNb 4O 11.5 (LZNO) has been found in the Nb-rich part of Li 2O–ZnO–Nb 2O 5 system. LZNO, with an original α-PbO 2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9) Å, b=15.2924(7) Å, c=5.0363(3) Å and γ=96.607(5)° or as α-PbO 2-like with lattice constants a=4.72420(3) Å, b=5.72780(3) Å, c=5.03320(3) Å, γ=90.048(16)° and modulation vector q=0.3 a *+1.1 b * indicating a commensurately modulated α-PbO 2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112 1 /n( αβ0)00) as well as a supercell (space group P2 1 /b). The superspace description allows us to consider the LZNO structure as a member of the proposed α-PbO 2- Z (3+1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li 2O–ZnO–Nb 2O 5 system are predicted on the basis of this detailed HRTEM analysis.

Subsolidus phase relations of the ZnO–Li 2O–P 2O 5 system

As a systematic search for suitable flux to grow zinc oxide single crystals, the subsolidus phase relations of the ternary system ZnO–Li 2O–P 2O 5 were investigated by means of X-ray diffraction (XRD). There are 6 binary compounds, 5 ternary compounds and 17 three-phase regions in this system. A new compound, Li 6Zn(P 2O 7) 2, is found in this system based on XRD experiments. The phase diagrams of the pseudo-binary systems Li 3PO 4–ZnO and LiZnPO 4–ZnO are investigated. It shows that the compounds, Li 3PO 4 and LiZnPO 4, are not suitable as flux for the growth of ZnO single crystals below 1250 °C.

Effect of different nucleation catalysts on the crystallization of Li 2O–ZnO–MgO–Al 2O 3–SiO 2 glasses

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO 2, Cr 2O 3, and ZrO 2 on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO 2 > Cr 2O 3 > ZrO 2. Virgilite, β-spodumene ss, gahnite, enstatite and cristobalite were formed in the prepared glass-ceramics. The microstructure of glass-ceramic samples showed growths of rounded and subrounded grains in the base sample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO 2. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO 2 and Cr 2O 3. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr 2O 3 > TiO 2 > ZrO 2) varying from 24.8 × 10 −7 to 65.1 × 10 −7 °C −1 being almost unchanged with the heat-treatment. The microhardness values of glass-ceramic samples were in the 763–779 kg/mm 2 range.

CdSe nanocrystals in novel phosphate glass matrix

The CdSe nanoparticles have been prepared in the novel glass matrix P 2O 5–Na 2O–ZnO–Li 2O. The prepared nanoparticles and glass matrix are characterized by differential thermal analysis, X-rays diffraction, UV–vis optical absorption, and infrared spectroscopy. X-rays diffraction and optical absorption show that both of the annealing temperature and time play an important role in nanoparticles’ growth. The well-annealed and high-temperature-annealed samples suggest Zn atoms to substitute Cd atoms to form an additional ZnSe–CdSe system. Infrared spectroscopy confirms the decrease of the Zn-content in the host glass due to growing of nanoparticles, causing long phosphate chains within.

Spectroscopic studies of Bi 2O 3–Li 2O–ZnO–B 2O 3 glasses

Raman and infrared spectroscopies have been employed to investigate the xBi 2O 3–(65 − x)Li 2O–20ZnO–15B 2O 3 glasses in order to obtain information about the competitive role of Bi 2O 3 and B 2O 3 in the formation of glass network. IR and Raman spectra show that these glasses are made up of [BiO 3] pyramidal and [BiO 6] octahedral units. The formation of Zn 2+ in tetrahedral coordination was observed. The average electronic polarizability of the oxide ion ( α O 2 − ), optical basicity ( Λ), and Yamashita–Kurosawa's interaction parameter ( A) were also examined.

Second-order optical non-linearity initiated in Li 2O–Nb 2O 5–SiO 2 and Li 2O–ZnO–Nb 2O 5–SiO 2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 Å have been formed in glasses of the Li 2O–Nb 2O 5–SiO 2 (LNS) and Li 2O–ZnO–Nb 2O 5–SiO 2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher T g lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO 3 and non-polar LiZnNbO 4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO 3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO 4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO 3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

Effect of heat-treatment condition on crystallization behavior and thermal expansion coefficient of Li 2O–ZnO–Al 2O 3–SiO 2–P 2O 5 glass–ceramics

Utilizing P 2O 5 as nucleation agent, a Li 2O–ZnO–Al 2O 3–SiO 2 glass was prepared by conventional melt quenching technique and subsequently converted to glass–ceramics with different crystal phases. During the processing, two-step heat-treatments including nucleation and crystallization were adopted. The effects of heat-treatment on the crystal type, the microstructure and the thermal expansion behavior of the glass–ceramics were studied by means of differential scanning calorimetry, X-ray powder diffraction analysis, scanning electron microscopy and thermal expansion coefficient tests. It was shown that the crystallization of β ∥ ′ - Li 2 ZnSiO 4 occurred after the glass was treated at 580 °C. As the temperature increased from 580 °C to 630 °C, cristobalite and β ∥ ′ - Li 2 ZnSiO 4 were identified as main and second crystal phases, respectively, in the glass–ceramic. An increase in the temperature to 700 °C, the β-quartz solid solution in the glass–ceramic accompanied by a decrease in cristobalite content. The transformation from β ∥ ′ - Li 2 ZnSiO 4 to γ 0-Li 2ZnSiO 4 took place from 700 °C to 750 °C. The resulting crystallization phases in the glass–ceramics obtained at the temperature higher than 750 °C were β-quartz solid solution and γ 0-Li 2ZnSiO 4. The glass–ceramics containing β ∥ ′ - Li 2 ZnSiO 4 or β-quartz solid solution crystal phase possessed a microstructure formed by the development of dendritic crystals. The thermal expansion coefficient of the glass–ceramics varied from 36.7 to 123.8 × 10 −7 °C −1 in the temperature range of 20–400 °C, this precise value is dependent on the type and the proportion of the crystalline phases presented.

Subsolidus phase relationships in the system ZnO–Li 2O–WO 3

The subsolidus phase relationships of the system ZnO–Li 2O–WO 3 have been investigated by X-ray diffraction (XRD) analyses. There are one ternary compound, five binary compounds and eight 3-phase regions in this system. The new ternary compound Li 2Zn 2W 2O 9 was found by the powder diffraction pattern. The corresponding crystal structure of this compound was refined by Rietveld profile fitting method. It belongs to a trigonal system with space group P 3 ¯ c 1 and lattice constants are a = 5.1438(2) Å, c = 14.1052(3) Å, and its thermal property was studied.

Use of CsCl to Enhance the Glass Stability Range of Tellurite Glasses for Er3+-Doped Optical Fiber Drawing

Tellurite glasses are important as a host of Er3+ ions because of their good solubility and because they present broadband optical gain compared with Er3+-doped silica, with the potential to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good-quality optical fibers. CsCl acts like a network modifier in glass systems, weakening the network by forming Te–Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi2O3 content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er3+-doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO2–ZnO–Li2O–Bi2O3–CsCl glasses.

Elastic properties and spectroscopic studies of fast ion conducting Li 2O [sbnd]ZnO [sbnd]B 2O 3 glass system

Glass systems of the composition xLi 2O–20ZnO–(80 − x)B 2O 3 where ( x = 5, 10, 15, 20, 25 and 30 mol%) have been prepared by melt quenching technique. Elastic properties, 11B MAS-NMR and IR spectroscopic studies have been employed to study the structure of Li 2O–ZnO–B 2O 3 glasses. Elastic properties have been investigated using sound velocity measurements at 10 MHz. Elastic moduli reveal trends in their compositional dependence. The bulk modulus and shear modulus increases monotonically with increase of BO 4 units, which increase the dimensionality of the network. 11B MAS-NMR and IR spectra show characteristic features of borate network and compositional dependent trends as a function of Li 2O/ZnO concentration. The results are discussed in view of borate network and the dual structural role of Zn 2+ ions. The results indicate that the Zn 2+ are likely to occupy network-forming positions in this glass system.

Ti3+‐Free Multicomponent Titanophosphate Glasses as Ecologically Sustainable Optical Glasses

Ti3+‐free multicomponent titanophosphate glasses were developed as ecologically sustainable optical glasses. Especially, recent advances in the glasses as molding glass, athermal glass, nonlinear optical glass, and self‐cleaning glass were presented. The Ti3+‐free binary TiO2–P2O5 glasses containing TiO2 up to 74 mol% were prepared by melt quenching and long‐term post‐annealing around the glass transition temperature in the air, and possessed high transparency, high index, high dispersion, and low density. Li2O–ZnO–TiO2–P2O5 glasses have the lowest Tg (=560°C) among titanophosphate glasses, with high index (nd=1.8), and high dispersion (νd=22) being retained, while ZnO–TiO2–P2O5 glasses have the highest refractive index (nd=1.9) among glasses with Tg lower than 600°C. Thus, ZnO–TiO2–P2O5 and Li2O–ZnO–TiO2–P2O5 glasses can be expected as high‐index molding glasses. A very small temperature coefficient of refractive index, dn/dT, or very small temperature coefficient of optical path length, dS/dT, was obtained for K2O–TiO2–P2O5 glasses, meaning that they are considered as high‐index athermal glasses and athermal NLO glasses. Ag2O–TiO2–P2O5 glasses showed photocatalytic activity and photo‐induced hydrophilicity comparable with commercially available TiO2‐coated self‐cleaning glasses.

Subsolidus phase relation in the system ZnO–Li 2O–MoO 3

The subsolidus phase relation of the system ZnO–Li 2O–MoO 3 has been investigated by X-ray diffraction (XRD) analyses. The phase diagram has been constructed. There are six binary compounds and one ternary compound in this system. The phase diagram comprises nine three-phase regions. The ternary compound Li 2Zn 2(MoO 4) 3 is refined by the Rietveld method. It belongs to an orthorhombic system with space group Pnma and lattice constants a = 5.1114 Å, b = 10.4906 Å, c = 17.6172 Å.