Increase In Ionic Radius Research Articles

Thermodynamics of Nanoscale Calcium and Strontium Titanate Perovskites

The surface enthalpies of nanocrystalline CaTiO3 and SrTiO3 perovskites were determined using high‐temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The nanocrystalline samples were synthesized by a hydrothermal method and characterized using powder X‐ray diffraction, FTIR spectroscopy, and Brunauer–Emmett–Teller surface area measurements. The integral heats of water vapor adsorption on the surfaces of nanocrystalline CaTiO3 and SrTiO3 are −78.63 ± 4.71 kJ/mol and −69.97 ± 4.43 kJ/mol, respectively. The energies of the hydrous and anhydrous surfaces are 2.49 ± 0.12 J/m2 and 2.79 ± 0.13 J/m2 for CaTiO3 and 2.55 ± 0.15 J/m2 and 2.85 ± 0.15 J/m2 for SrTiO3, respectively. The stability of the perovskite compounds in this study is discussed according to the lattice energy and tolerance factor approach. The energetics of different perovskites suggest that the formation enthalpy becomes more exothermic and surface energy increases with an increase in ionic radius of the “A” site cation (Ca, Sr, and Ba), or with the tolerance factor. PbTiO3 shows a lower surface energy, weaker water binding, and a less exothermic enthalpy of formation than the alkaline‐earth perovskites.

Promising wastewater treatment using rare earth-doped nanoferrites

Single-phases of the spinel nanoferrites Zn0.5Co0.5Al0.5R0.04Fe1.46O4; R=Sm, Pr, Ce and La, were synthesized using the flash auto combustion method. X-ray diffraction (XRD) results indicated that doping nanoferrites with small concentrations of rare earth elements (RE) allowed their entrance to the spinel lattice. Transmission electron microscope (TEM) images revealed that doping with different RE elements resulted in the formation of different nanometric shapes such as nanospheres and nanowires. Doping with Sm3+ and Ce3+ resulted in the formation of nanospheres with average diameter of 14 and 30nm respectively. In addition to the granular nanospheres, doping with Pr3+ and La3+ resulted in the formation of some nanowires with different aspect ratios (average length of ≈100nm and diameter of ≈9nm) and (average length of ≈150nm and outer diameter of ≈22nm) respectively. At fixed temperature, the Ac conductivity (σ) increased as the RE ionic radius increases except for Ce, due to the role of valance fluctuation from Ce3+ to Ce4+ ions. La- and Pr-doped nanoferrites showed the highest ac conductivity values, which is most probably due to the presence of large numbers of nanowires in these two types of ferrites. For all entire samples, the effective magnetic moment (μeff) decreased, while the Curie temperature (TC) increased as the RE ionic radius increases. The synthesized rare earth nanoferrites showed promising results in purifying colored wastewater. La-doped ferrite was capable for up-taking 92% of the dye content, followed by Pr-doped ferrite, which adsorbed 85% of the dye, while Sm- and Ce-doped ferrites showed lower dye removal efficiency of 80% and 72% respectively. High dye uptake shown by La- and Pr-doped ferrites is most probably due to the presence of nanowires and their higher Ac conductivity values. These excellent results were not previously reported.

Rotational and translational distortions of the crystal structure of the Sr2HrRuO6 (Hr = Ho, Dy, Gd, Eu) complex perovskites

Sr2HrRuO6 (Hr = Ho, Dy, Gd, Eu) complex perovskites were synthesized through the high-temperature solid-state reaction method, and their crystal structures were analyzed in detail as a function of the Hr-cation ionic radius. Results of powder XRD pattern measurement and Rietveld analysis of the experimental profiles show that the Sr2HrRuO6 compounds crystallize in a monoclinic distorted perovskite-like structure, P21/n (#14) space group, where the unit cell parameters are related to the primitive unit cell ap by a≈2ap, b≈2ap and c ≈ 2ap. The structures show an alternate distribution of the Ru5+ (2d: 0.5, 0, 0) and Hr3+ (2c: 0, 0.5, 0) making up RuO6 and HrO6 octahedra alternatively arranged in two interleaving fcc sublattices, where the O(1), O(2), and O(3) ions are localized at the corner of the octahedral, while the Sr2+ is located at the A-site, occupying the cavities built by the corner-sharing octahedra with Wyckoff position 4e. Due to the existence of mismatched ionic sizes between the ionic radii of the Sr2HrRuO6 compounds, the HrO6 and RuO6 octahedra are constrained to tilting around the [111]c, [001]c, and [110]c cubic directions so as to optimize the Sr–O inter-atomic bond lengths, tending to rotate the structure in order to fix the Ru5+ and Hr3+ ions on the M′ and M″ sites of the complex perovskites. The cell parameters a, b, and c, the inter-atomic bond angles, the inter-atomic bond lengths, and the tilting angles increase as the Hr-cation ionic radius increases. The mismatch that exists in the Sr2HrRuO6 ionic radius produces a large distortion from the ideal cubic symmetry. The pure perovskite-like phase of Sr2HrRuO6 is thermodynamically and kinetically stable at high temperatures above 1420 K, where it is entirely governed by the average size of the Hr3+ and Ru5+ cations.

Microwave dielectric characteristics of Li2(Mg0.94M0.06)Ti3O8 (M=Zn, Co, and Mn) ceramics

Abstract Li2(Mg0.94M0.06)Ti3O8 (M=Zn, Co, and Mn) ceramics were synthesized by the conventional solid-state reaction route. The effect of M (Zn, Co, and Mn) substitution on the structure, microstructure and microwave dielectric properties of Li2(Mg0.94M0.06)Ti3O8 has been investigated. The XRD patterns of sintered samples revealed the single-phase formation with spinel structure. With the increase in ionic radius of M, the Qf value decrease is attributed to the decrease of packing fraction and grain size. The Li2(Mg0.94Zn0.06)Ti3O8 ceramic sintered at 1075 °C for 4 h showed the best microwave dielectric properties with a dielectric constant of 27.1, a Qf value of 44 800 GHz, and a temperature coefficient of resonant frequency of (+)1.9 ppm/°C.

Spectral study on one-electron-oxidized di(phthalocyaninato)rare-earths(III)

Nine double-decker bis(phthalocyaninato)rare-earth(III) complexes, [M(pc)2] (green radical species; M = Sc, Y, La, Pr, Sm, Eu, Tb, Ho, Yb ) have been electrochemically and spectro-electrochemically investigated in CH2Cl2 . All of them show one oxidation and three reduction waves, which involve phthalocyanine macrocycles. Apart from the lanthanum derivative, the first oxidation and reduction potentials show linear cathodic shift with an increase in ionic radius of the central metal (ri), whereas the second and third reduction little depend on ri. Electrochemical oxidation (around the oxidation potential) and chemical oxidation produced the same red~orange species (depending on the central metal). Their optical absorption spectra show three characteristic bands in 400~600, 600~750, and 800~1200 nm in visible and near-infrared region and their peak positions (in cm-1) linearly depend on ri (except for La). Assignment of these bands has been done based on magnetic circular dichroism spectroscopy and the electrochemical data.

Alkali Metal and Zinc Complexes of a Bridging 2,5-Diamino-1,4-Benzoquinonediimine Ligand

Two alkali metal complexes of a bridging 2,5-diamino-1,4-benzoquinonediimine ligand (dipp-dabqdiH(2)), [(thf)(2)Li(μ-dipp-dabqdi)Li(thf)(2)] (1) and [(dme)(1.5)Na(μ-dipp-dabqdi)Na(dme)(1.5)](n) (2, dme = 1,2-dimethoxyethane), have been synthesized by the reaction of dipp-dabqdiH(2) with Li(n)Bu or sodium metal. In addition, treatment of 1,2,4,5-tetrakis(2,6-diisopropylamino)benzene (dipp-tabH(4)) with potassium metal in dme afforded the complex [(dme)(2)K(μ-dipp-tabH(2))K(dme)(2)] (3). X-ray crystal diffraction analyses revealed that complexes 1 and 3 have dinuclear structures, while the sodium complex 2 aggregates to a one-dimensional polymer through bridging dme ligands. With increasing ion radius, the coordination number of the alkali metal (Li, Na, and K) increases from four to five to six, while the coordination geometry changes from distorted tetrahedral to square pyramidal and further to octahedral in 1, 2, and 3, respectively. The salt metathesis reactions of 1 and 2 with anhydrous ZnCl(2) yielded the ion-contacted zinc complexes [(thf)(3)Li(μ-Cl)ClZn(μ-dipp-dabqdi)ZnCl(μ-Cl)Li(thf)(3)] (4), [(dme)(2)Li(μ-Cl)ClZn(μ-dippdabqdi)ZnCl(μ-Cl)Li(dme)(2)] (5), and [(dme)(2)Na(μ-Cl)(2)Zn(μ-dipp-dabqdi)Zn(μ-Cl)(2)Na(dme)(2)] (6), respectively. The ligand exists as the dianionic form in compounds 1-6 upon double deprotonation, and a complete electronic delocalization (except for 3) of the quinonoid π-system is observed between the metal centers over the two N═C-C═C-N halves of the ligand. The electronic structures of the complexes were studied by density functional theory (DFT) computations.

Super broadband near infrared luminescence properties in Bi-doped aluminosilicate glasses

Influences of alkaline earth oxides on super broadband near infrared luminescence properties from Bi-doped RO-Al2O3-SiO2 (R=Ca, Sr, Ba) aluminosilicate glasses are investigated. The results show that under different pumping sources, the near infrared (NIR) luminescence shows different behaviors. Under 808 nm excitation, the infrared emission located at 1300 nm with lifetime more than 600 ms is observed, whose intensity increases with the increase of ionic radius. However, under 690 nm excitation, the luminescence at 1100 nm with a full width at half maximum of 400 nm decreases with the increase of ionic radius. According to the above results, it is suggested that infrared emissions may originate from Bi+ and BiO.

Lanthanide dopant-induced phase transition and luminescent enhancement of EuF3 nanocrystals

A novel strategy is proposed to prepare hexagonal EuF3 nanocrystals by doping lanthanide ions (Ln3+) with large ionic radius (such as La3+, Ce3+, Pr3+, Nd3+ and Sm3+). Complete phase transition from orthorhombic to hexagonal phase can be achieved with the increase of ionic radius or doping concentration of Ln3+ ions. Meanwhile, the size and self-assembly degree of the product can be reduced dramatically. The possible growth and phase transformation mechanism of EuF3 nanocrystals was proposed. Finally, Eu3+ ion was used as the structural probe to investigate the effect of phase transition on the luminescence. It was found that the emissions of the 5D0 level of Eu3+ are greatly enhanced with the phase transition from orthorhombic to hexagonal phase. The luminescent enhancement is attributed to the larger radiative transition rate of the 5D0 level in the environment with lower symmetry, which can be confirmed by Judd–Ofelt (J–O) theory.

Ferroelectric phase transition and low-temperature dielectric relaxations in Sr4(La1−xSmx)2Ti4Nb6O30 ceramics

Ferroelectric transition and the low-temperature dielectric relaxations were investigated in Sr4(La1−xSmx)2Ti4Nb6O30 ceramics. The dielectric nature of the present ceramics was governed by the radius difference between A1- and A2-site ions. Low-temperature dielectric relaxations were indicated for all the compositions, and the diffuse ferroelectric peak appeared gradually with increasing x (increasing ion radius difference between A1- and A2-sites), and it became the normal ferroelectric one for x = 1. There was no peak on the differential scanning calorimetry (DSC) curves for the compositions with x = 0, 0.25, 0.5, and 0.75, while an obvious endothermic peak was observed for x = 1. Based on the analysis of the dielectric data and the DSC results, the ferroelectric transition for x = 1 was determined as a first order phase transition, and the second order phase transition was suggested for other compositions.

Spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films

We present the results of an optical method of quantitatively estimating the spin exchange interactions in hexagonal manganites RMnO3 (R = Tb, Dy, Ho, Er) epitaxial thin films. The two in-plane (a-b plane) spin exchange integrals J1 (intratrimer Mn-Mn interaction) and J2 (intertrimer Mn-Mn interaction) are deduced from the magnon scattering peak wavenumbers. We found that J2 decreases systematically when the R ionic radius increases, while J1 is nearly independent of R ionic radius, contrary to the expectation in single crystals. We show that the R dependence of J1 could be understood in terms of the stress in the thin films. Our result indicates that the stress has stronger effect on the atomic displacement of the intratrimer Mn-Mn distance than the intertrimer Mn-Mn distance.

Synthesis using molten KOH and properties of rare earth substituted REBa2Cu4O8 phases

Rare-earth-substituted REBa2Cu4O8 phases (RE124) are synthesized by using molten KOH to investigate phase formation and superconductivity. RE124 phases with small and heavy rare-earth elements of Yb, Er, Ho, Dy, Gd and Y are easily producible with good superconducting properties and crystallinity. Superconducting transition temperature and superconducting volume fraction decrease with increasing ion radius of the rare-earth elements. Samples using large rare-earth elements show broad peaks of RE124 pattern in x-ray diffraction also with broad peaks probably originating from RE123 and other related phases.

Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition.

Aminotroponiminate Complexes of the Heavy Alkaline Earth and the Divalent Lanthanide Metals as Catalysts for the Hydroamination/Cyclization Reaction

Reaction of SrI2, EuI2(THF)2, and YbI2(THF)2 with KN(SiMe3)2 and [{(iPr)2ATI}K] ((iPr)2ATI = N-isopropyl-2-(isopropylamino)troponiminate) led to monoaminotroponiminate complexes of the heavier alkaline earth elements and the related divalent lanthanides of composition [{(iPr)2ATI}M{N(SiMe3)2}(THF)2)] (M = Sr, Eu, Yb). Diaminotroponiminate complexes of composition [{(iPr)2ATI}2M(THF)2)] (M = Sr, Ba) were obtained by the reaction of SrI2 and BaI2 with 2 equiv of [{(iPr)2ATI}K]. All new compounds were characterized by single-crystal X-ray diffraction. Independent of the ionic radius of the center metal all monoaminotroponiminate complexes [{(iPr)2ATI}M{N(SiMe3)2}(THF)2] including the previously reported Ca analogue are isostructural. The same phenomenon is observed for [{(iPr)2ATI}2M(THF)2)]. The heterolepetic compounds [{(iPr)2ATI}M{N(SiMe3)2}(THF)2)] were used as catalysts for the intramolecular hydroamination/cyclization reaction of nonactivated aminoalkenes. A decrease in the rate with increasing ion radius of the center metal is observed for the alkaline earth elements. The ytterbium complex, which is oxidized during the catalytic conversion, is also an efficient precatalyst for the hydroamination/cyclization reaction.

Role of rare earth oxide coatings on oxidation resistance of chromia-forming alloys

Rare earths (RE) have been used to increase high temperature oxidation resistance of chromia and alumina forming alloys. The RE can be added as elements (or oxides) to the alloys or applied as oxide coatings to the alloy surface. This paper presents the effect of different RE oxide coatings and lanthanum chromite coatings on the high temperature oxidation behavior of Fe20Cr and Fe20Cr4Al alloys. The oxidation resistance of the Fe20Cr alloy increased with increase in ionic radius of the RE element in the coating. The RE oxides decreased chromia growth rate more than alumina growth rate. In extended cyclic oxidation tests that were carried out from peak temperatures of 900 °C, 1,000 °C and 1,100 °C to room temperature at cooling rates of 300 °C/s and 1,000 °C/s, the La2O3 coating increased cyclic oxidation resistance of the Fe20Cr alloy significantly more than the Pr2O3 coating. The role of RE in increasing overall oxidation resistance of chromia forming alloys is discussed.

Size Selective Extraction of N,N,N′,N′-Tetraoctyldiglycolamide and the Structure of Its Divalent Metal Complex

Abstract Using a new extractant, N,N,N′,N′-tetraoctyldiglycolamide (TODGA), the dependence of the distribution ratio on the ionic radii for MII was investigated, and their relation with the structures of metal complexes were discussed. CaII (ionic radius: 100 pm) shows the highest D values, and the D values decrease with increase and decrease of ionic radius from 100 pm. The geometrical optimization by density functional theory (DFT) of MII–TODGA complex suggests that the carbonyl oxygen has more affinity with metal than the ether oxygen, and the distance between the center of oxygen donor and the edge of cation corresponds to the van der Waals radius of oxygen atom. The most stable complex, as 1:1 complex, can be formed with MgII from DFT calculation, the complex becomes unstable with increase of ionic radius of MII. This order is good agreement with the magnitude of D for CaII, SrII, and BaII.

Phase composition of the ceramics based on Rare Earth, Manganese and Titanium Oxides

ABSTRACTCeramics in systems with rare earth (REE = Y, Sm, Gd), manganese, and titanium oxides are considered as potential matrices for immobilization of REE- and actinide-containing radioactive wastes. Ceramics of this type were synthesized from oxide mixtures by a cold pressing and sintering method at temperatures of 1300-1400 °C as well as plasma heating. Major phases in the ceramics were found to be the phases of the pyrochlore-murataite polysomatic series with three- (3C), five- (5C), and seven-fold (7C) elementary fluorite unit cell. Perovskite/pyrophanite, hibonite/loveringite as well as garnet in the samples contained extra Fe and Al oxides were present as minor phases. Formation of the murataite, to be exact – structures built from murataite and pyrochlore modules, is more characteristic of the Y-bearing systems rather than the systems with heavier lanthanides. Increase of ionic radius of the REE trends towards formation of the pyrochlore structure phases whereas occurrence of large-size cations (La) stimulates formation of the perovskite structure phase. In the Y-bearing system murataite formation takes place at relative low Y2O3 concentrations (<15 mole %) and TiO2 content as high as ∼60 mole % and MnOx – 15-20 mole %. Higher Y2O3 concentrations and Gd2O3 substitution for Y2O3 yields preferably the pyrochlore phase or may favor formation of the phase with the 7C polytype.

Pb and rare earth element diffusion in xenotime

Diffusion of Pb and the rare earth elements Sm, Dy and Yb have been characterized in synthetic xenotime under dry conditions. The synthetic xenotime was grown via a Na 2CO 3–MoO 3 flux method. The sources of diffusant for the rare earth diffusion experiments were REE phosphate powders, with experiments run using sources containing a single REE. For Pb, the source consisted a mixture of YPO 4 and PbTiO 3. Experiments were performed by placing source and xenotime in Pt capsules, and annealing capsules in 1 atm furnaces for times ranging from 30 min to several weeks, at temperatures from 1000 to 1500 °C. The REE and Pb distributions in the xenotime were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relations are obtained for diffusion in xenotime, normal to (101): D Sm = 1.5 × 10 − 4 exp ⁡ ( − 441 ± 12 kJmol − 1 / R ⁢ T ) m 2 s − 1 . D Dy = 9.0 × 10 − 8 exp ⁡ ( − 349 ± 16 kJmol − 1 / R ⁢ T ) m 2 s − 1 . D Yb = 3.9 × 10 − 7 exp ⁡ ( − 362 ± 13 kJmol − 1 / R ⁢ T ) m 2 s − 1 . Diffusivities among the REE do not differ greatly in xenotime over the investigated temperature range, in contrast to findings for the REE in zircon [Cherniak, D.J., Hanchar, J.M., Watson, E.B., 1997. Rare earth diffusion in zircon. Chem. Geol. 134, 289–301.], where the LREE diffuse more slowly, and with higher activation energies for diffusion, than the heavier rare earths. In zircon, these differences among diffusion of the rare earths are attributed to the relatively large size of the REE with respect to Zr, for which they likely substitute in the zircon lattice. With the systematic increase in ionic radius from the heavy to lighter REE, this size mismatch becomes more pronounced and diffusivities of the LREE are as consequence slower. Although xenotime is isostructural with zircon, the REE are more closely matched in size to Y, so in xenotime this effect appears much smaller and the REE diffuse at similar rates. In addition, the process of diffusion in xenotime likely involves simple REE + 3 → Y + 3 exchange, without charge compensation as needed for REE + 3 → Zr + 4 exchange in zircon. This latter factor may also contribute to the large activation energies for diffusion of the REE in zircon (i.e., 691–841 kJ mol − 1 , [Cherniak, D.J., Hanchar, J.M., Watson, E.B., 1997. Rare earth diffusion in zircon. Chem. Geol. 134, 289–301.]), in comparison with those for xenotime. For Pb, the following Arrhenius relation is obtained (also normal to (101)): D Pb = 3.0 × 10 − 9 exp ⁡ ( − 382 ± 64 kJmol − 1 / R ⁢ T ) m 2 s 1 . These measurements suggest that Pb diffusion in xenotime is quite slow, even slower than Pb diffusion in monazite and zircon, and considerably slower than diffusion of the REE in xenotime. Xenotime may therefore be even more retentive of Pb isotope signatures than either monazite or zircon in cases where Pb isotopes are altered solely by volume diffusion. However, because the activation energy for Pb diffusion in xenotime is lower than those for monazite and zircon, Pb diffusion may be somewhat faster at many temperatures of geologic interest in xenotime than in monazite or zircon.

Immobilization of Harmful Metallic Elements in HZr2(PO4)3

Several harmful metal ions (M=Mn(II), Cu(II), Zn(II), Cd(II) and Pb(II)) were completely immobilized in the crystalline zirconium phosphate, HZr2(PO4)3, by thermal-treating the mixture of M(NO3)2 and HZr2(PO4)3 under the molar ratios of M(NO3)2/HZr2(PO4)3=0.1-0.5 at 700°C for 5 h. The XRD analyses suggested that all the M(II) immobilized products have the same structure as that of the NASICON-type HZr2(PO4)3. Such immobilized products were subjected to the leaching test of M(II) ion in 1 mol•dm-3 HCl at 160°C for 24 h. For the M(II) immobilized products with the ratio of M(NO3)2/HZr2(PO4)3=0.5, the leaching rate was decreased with the increase in ionic radius of M(II).

Effect of Alkali Ions on the Optical Absorption Characteristics of Co2+ ion in Binary Silicate Glasses

Co2+ ion was found to produce a variety of colour shades ranging form pinkish blue to intense blue to greenish blue in a series of binary alkali silicate glasses. The optical absorption characteristics of divalent cobalt produce three strong bands in the visible and two weak bands in the near infrared region, respectively in lithium silicate, sodium silicate and potassium silicate glasses. In the present study, the molar extinction coefficients of Co2+ ion were calculated using Bouger-Beer's equation and the intensities of the bands were reported quantitatively in glasses at their wavelength maxima. The absorption bands in the molar extinction curves for Co2+ ion were found to shift more towards longer wavelengths with an increase in ionic radius of alkali ion on replacing lithium by sodium and sodium by potassium in glasses. The results were explained with reference to Ilse and Hartmann equation. Further, the values of molar extinction coefficients were found to increase with increasing basicity of the alkali silicate glasses as ionic radii of the alkali ions increase in order of K+> Na+> Li+ in the glass.

New alkali antimonate glasses

Glass formation has been investigated in ternary systems Sb 2O 3–PbO–M 2O in which M is alkali Li, Na and K and antimony oxide is the glass former. Alkali elements were introduced as carbonates. The size of the glass forming region is enlarged as alkali ionic radius increases. Binary Sb 2O 3–M 2O glasses were obtained: (100− x) Sb 2O 3– xLi 2O, (10< x<30), (100− x) Sb 2O 3– xNa 2O, (10< x<70), and (100− x) Sb 2O 3– xK 2O, (10< x<90). In ternary systems, PbO content could reach 60 mol%. Temperatures of glass transition, T g, onset of crystallization, T x, and maximum of crystallization, T p, have been measured using differential scanning calorimetry. Depending on composition, glass transition temperature ranges from 240 to 330 °C. The incorporation of alkali oxide increases T g while lead oxide has the reverse effect. Thermal stability range ( T x– T g) was usually between 65 and 266 °C, while no crystallization exotherm was observed in some cases. Density and thermal expansion increases as lead concentration increases. Optical transmission has been measured. The UV cut-off depends on alkali content: samples are yellow and turn green for large K and Na content. These glasses have potential applications as low phonon energy glasses for infrared transmission or active devices.