Thermal,Structural, and Crystallization Properties of New Tantalum Alkali‐Germanate Glasses

In this work, new glass compositions were prepared in the ternary system GeO₂–K₂O–Ta₂O₅. Potassium oxide was added to reach the complete melt of the starting mixture and two composition series were investigated: the first one with a constant K₂O molar content of 10% in the ternary system (90–x)GeO₂–10K₂O–xTa₂O₅ and the second one with the same molar content of K₂O and Ta₂O₅ in the ternary system (100–2x)GeO₂–xK₂O–xTa₂O₅. Homogeneous and transparent glasses could be obtained between x = 0 and 20. X‐ray diffraction analyzes of samples with x = 25 identified orthorhombic Ta₂O₅ in the first series and an isostructure of K_3.8Ge₃Nb₅O_20.4 in the second series where it is assumed that Ta⁵⁺ ions are inserted in the Nb⁵⁺ sites. As one of our goal with these materials is related with the preparation of glass‐ceramics containing Ta₂O₅ nanocrystals, the first series has been selected for further characterizations. An increase in glass‐transition temperatures with increasing Ta₂O₅ content as well as an increase of the thermal stability from x = 0 to 10 has been identified by differential scanning calorimetry. For higher contents, crystallization events were identified. Fourier transform infrared and Raman spectroscopic characterizations allowed to point out the intermediary behavior of Ta₂O₅ in the vitreous network where TaO₆ octahedra are inserted inside the germanate network with TaO₆ clusters identified at higher Ta₂O₅ contents. Heat‐treated samples with high tantalum contents (x = 15 and 20) exhibit preferential precipitation of orthorhombic Ta₂O₅ with nanometric size, suggesting the possibility of obtaining transparent glass‐ceramics for optical applications.     

Structural and Textural Modifications of Ternary Phosphate Glasses by Thermal Treatment

Phosphate-based glasses of composition xNa₂O−(45+(10−x))CaO−45P₂O₅ with different Na₂O, CaO (x = 1, 5, 10, 15, and 20 mol%), and invariable P₂O₅ (45 mol%) contents were prepared using the rapid melt quench technique. The obtained thermal data from differential thermal analysis revealed a decline in glass transition (T_g) and crystallization (T_c) temperatures of glasses against the compositional changes. The inclusion of Na₂O at the cost of CaO in the glass network led to a reduction in its thermal stability. The thermal treatment carried out on glasses helped to derive their glass-ceramic counterparts. The amorphous and crystalline features of samples were characterized using X-ray diffraction patterns. The crystalline species that emerged out of the calcium phosphate phases confirmed the dominance of Q¹ and Q² structural distributions in the investigated glass-ceramics. The obtained scanning electron micrographs and atomic force microscopic images confirmed the surface crystallization and textural modification of the samples after thermal treatment. The N₂-adsorption–desorption studies explored the reduction of porous structures due to thermal treatment on the melt-driven glass surface. The measured elastic moduli and Vicker's hardness values of the glasses showed an increase after thermal treatment, which were reduced against the inclusion of alkali content in both glass and glass-ceramics.     

High niobium oxide content in germanate glasses: Thermal,structural, and optical properties

Niobium alkali germanate glasses were synthesized by the melt‐quenching technique. The ternary system (90‐x)GeO₂–xNb₂O₅–10K₂O forms homogeneous glasses with x ranging from 0 to 20 mol%. Samples were investigated by DSC and XRD analysis, FTIR and Raman spectroscopy, and optical absorption. Structural and physical features are discussed in terms of Nb₂O₅ content. The niobium content increase in the glass network strongly modifies the thermal, structural and optical properties of alkali germanate glasses. DSC, Raman and FTIR analysis suggest niobium addition promotes NbO₆ groups insertion close to GeO₄ units of the glass network. XRD analysis also pointed out that samples containing high niobium oxide contents exhibit preferential niobium oxide‐rich phase after crystallization after heat treatment, which is similar to orthorhombic Nb₂O₅. Absorption spectra revealed high transmission range between 400 nm to 6.2 μm, added to a considerably decreased hydroxyl group content as the addition of niobium in the alkali germanate network. The niobium oxide‐rich phase crystallization process was studied and activation energy was determined, as well as nucleation and crystal growth temperatures and time for obtaining transparent glass‐ceramics.     

Hydrogen spillover phenomenon: Enhanced reversible hydrogen adsorption/desorption at Ta2O5-coated Pt electrode in acidic media

The current study is concerned with the preparation and characterization of tantalum oxide-loaded Pt (TaO_x/Pt) electrodes for hydrogen spillover application. XPS, SEM, EDX and XRD techniques are used to characterize the TaO_x/Pt surfaces. TaO_x/Pt electrodes were prepared by galvanostatic electrodeposition of Ta on Pt from LiF-NaF (60:40 mol%) molten salts containing K₂TaF₇ (20 wt%) at 800 °C and then by annealing in air at various temperatures (200, 400 and 600 °C). The thus-fabricated TaO_x/Pt electrodes were compared with the non-annealed Ta/Pt and the unmodified Pt electrodes for the hydrogen adsorption/desorption (H_ads/H_des) reaction. The oxidation of Ta to the stoichiometric oxide (Ta₂O₅) increases with increasing the annealing temperature as revealed from XPS and X-ray diffraction (XRD) measurements. The higher the annealing temperature the larger is the enhancement in the H_ads/H_des reaction at TaO_x/Pt electrode. The extraordinary increase in the hydrogen adsorption/desorption at the electrode annealed at 600 °C is explained on the basis of a hydrogen spillover-reverse spillover mechanism. The hydrogen adsorption at the TaO_x/Pt electrode is a diffusion-controlled process.     

Growth of multioxide planar film with the nanoscale inner structure via anodizing Al/Ta layers on Si

An Al/Ta bilayer specimen prepared by a successive sputter-deposition of a 150-nm tantalum layer and a 180-nm aluminium layer onto a silicon wafer is anodically processed in a sequence of steps in oxalic acid electrolytes, at voltages of up to 53 V, which generates a 260-nm alumina film with well-ordered nanoporous structure. Further potentiodynamic reanodizing the specimen to 220 V causes the simultaneous growth of a 65-nm tantalum oxide layer beneath the alumina film and an array of oxide ‘nanocolumns’ (∼50 mn wide, ∼80 nm apart, ∼7 × 10⁹ cm⁻² population density) penetrating the alumina pores and reaching precisely to the top of the alumina film. The complete filling of the alumina pores is assisted by the high Pilling-Bedworth ratio for Ta/Ta₂O₅ and a substantially increased transport number for tantalum species (0.4), which is an average value of all migrating tantalum ions with different oxidation states. The nanocolumns are shown to be composed of a unique, regular mixture of Ta₂O₅ (dominating amount), suboxides TaO₂ and TaO_x (0.5 < x < 1), Al₂O₃, metallic Ta and Al aggregates, tantalum diboride (TaB₂) and oxidized boron from the electrolyte. The ionic transport processes determining the self-organized growth of these planar oxide nanostructures are considered and described conceptually.     

Large-scale synthesis of centrifugally spun tantalum oxynitride fiber electrocatalysts for hydrogen evolution reaction

Tantalum oxynitride (TaO_xN_1−x) fibers were synthesized and evaluated for their electrocatalytic hydrogen activity using an in-house developed centrifugal spinning setup. By tailoring the composition of the spinning solution and optimizing collector distance and rotation speed of the spinneret, bead-free TaO_xN_1−x fibers with a diameter of 800 nm were obtained. The fibers were structurally characterized through phase and elemental analysis, confirming the formation of monoclinic TaO_xN_1−x with clear splitting of the X-ray photoelectron spectroscopy peaks indicating Ta was in +5 oxidation state. The resulting oxynitride fibers exhibited superior electrocatalytic performance with low overpotentials (250 mV) to generate 10 mA/cm² compared to Ta₂O₅ oxide fibers. Interestingly, the enhanced activity of oxynitride fibers was observed to be suppressed in basic medium due to the high oxophilicity of tantalum ions and a negative Gibbs adsorption-free energy, leading to poisoning of the active sites. This work demonstrates a facile pathway for the fabrication of high-performance electrocatalysts, based on TaO_xN_1−x fibers, from a cost-effective and energy-efficient centrifugal spinning technique.     

Effect of Ta2O5 Substituting on Thermal and Optical Properties of High Refractive Index La2O3–Nb2O5 Glass System Prepared by Aerodynamic Levitation Method

High refractive index glasses with nominal composition of 0.35La₂O₃–(0.65?x)Nb₂O₅–xTa₂O₅ (x ≤ 0.35) were prepared by aerodynamic levitation method. The effect of Ta₂O₅ substituting on their thermal and optical properties was investigated. All the glasses obtained were colorless and transparent. Differential thermal analyzer results show that as the content of Ta₂O₅ increased, the thermal stability of the glasses increased but the glass‐forming ability decreased. The transmittance spectra of all the obtained glasses exhibited a wide transmittance window ranging from 380 to 5500 nm. As the content of Ta₂O₅ increased, the refractive index of the glasses was enhanced from 2.15 to 2.21 and the dispersion was reduced with the Abbe number increasing from 20 to 27.     

High‐Temperature Phase Relations in the Lu2O3–Ta2O5 System

The compounds formed from the Lu₂O₃–Ta₂O₅ system in the composition range 25–60 mol% Ta₂O₅ were prepared by solid‐state reaction from 1350°C to 2058°C, and the phase transitions were investigated by X‐ray diffraction (XRD). Cubic Lu₃TaO₇, M′‐LuTaO₄, M‐LuTaO₄, O‐Ta₂O₅, and T‐Ta₂O₅ are observed. With the temperature increase, there is an irreversible phase transition from M′ to M‐LuTaO₄ near 1770°C in the composition of 30–52 mol% Ta₂O₅, and another phase transition from T‐Ta₂O₅ to O‐Ta₂O₅ at about 1685°C when the ratio of Ta₂O₅ is >52 and ≤60 mol%. A phase diagram of the Lu₂O₃–Ta₂O₅ system in the range 0–100 mol% Ta₂O₅ was constructed. These results are helpful to explain the phase transition of Lu₂O₃–Ta₂O₅ system and design the preparation technique of LuTaO₄ single crystal or ceramic scintillator, which may be applied in the fields of nuclear medicine and high‐energy physics.     

Optimization thermophysical properties of TiO2 alloying Sm3TaO7 ceramics as promising thermal barrier coatings

TiO₂ alloying effect is applied to optimize the thermophysical properties of fluorite-type Sm₃TaO₇ ceramics synthesized via solid-state reaction, and the influence of TiO₂ alloying effect on the optical properties and elastic modulus is determined. According to the decreasing unit cell volume calculated by the X-ray diffraction and the broadening Raman peak, Ti⁴⁺ substitutes the same number of Sm³⁺ and Ta⁵⁺ ions of Sm₃TaO₇ ceramics at the same time. As Ti⁴⁺ substitutes Sm³⁺ and Ta⁵⁺ ions, the band gap of TiO₂-Sm₃TaO₇ ceramics decreases from 4.71 to 4.11 eV. The phase transition of Sm₃TaO₇ ceramics is eliminated by TiO₂ alloying effect and the coefficient of thermal expansion is increased. Via TiO₂ alloying effect, two different phonon scattering mechanisms: (a) the misfit of atomic weight and ionic radius among Ti⁴⁺, Sm³⁺, and Ta⁵⁺ ions; (b) the rattling Ti⁴⁺ ions are introduced in Sm₃TaO₇ ceramics. The lowest thermal conductivity of TiO₂-Sm₃TaO₇ ceramics reaches 1.37 W K⁻¹ m⁻¹ (800°C, 9 mol% TiO₂-Sm₃TaO₇), which is much lower than 7YSZ and Sm₂Zr₂O₇ ceramics. Accordingly, it is believed that TiO₂-Sm₃TaO₇ ceramics are promising thermal barrier coatings.     

Interactions of Ta2O5 with water vapor at elevated temperatures

Tantalum pentoxide (Ta₂O₅) and its solid solution phases are candidate coatings for components to be used in combustion environments. Thus, it is important to understand the response of Ta₂O₅ to high‐temperature water vapor, a product of combustion. Thermogravimetric methods are used to examine the oxide in reactant streams of controlled water vapor contents at 1250°C‐1450°C. The observed weight loss indicates a reaction of the general form ½ Ta₂O₅(s) + x H₂O(g)=TaO_y(OH)_x(g). Methodical variation in the water vapor pressure suggests the products are a mix of TaO(OH)₃(g) and Ta(OH)₅(g). Evidence of TaO(OH)₃(g) was observed with a sampling mass spectrometer. The measured hydroxide and oxyhyroxide vapor fluxes from Ta₂O₅ are compared with calculated vapor fluxes from SiO₂ and Al₂O₃. Ta₂O₅ exhibits fluxes similar to those from SiO₂ due to gaseous metal hydroxide formation.     

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

Tantalum silicate glasses serve as laser host materials to take advantage of their high refractive index and the ability to tailor their physical properties in the design of high-performance photonic and photoelectric components. However, successful attainment of feature control in tantalum-doped materials remains a longstanding problem due to the limited understanding of local structure around the tantalum ions, a problem that lies at the heart of predicting the micro- and macroscopic properties of these glasses. Herein, we present a novel approach for predicting the local structural environments in tantalum silicate glass based on a phase diagram approach. The phase relations and glass formation region of Li₂O–Ta₂O₅–SiO₂ ternary systems are explored to calculate the structure and additive physical properties of lithium tantalum silicate glasses. These measured and calculated results are in good quantitative agreement, indicating that the phase diagram approach can be applied broadly to Li₂O–Ta₂O₅–SiO₂ ternary glass systems. Using the phase diagram approach, the local structure of tantalum can be directly obtained. Each Ta atom is surrounded by six atoms, and its polyhedron, the TaO₆ octahedron, bonds through oxygen to Li and Ta. As a network modifier, Ta⁵⁺ depolymerizes the silicate glass structure by modulating the local structure of lithium atoms in Li₂O–Ta₂O₅–SiO₂ ternary glass system. The compositional dependence of structure in lithium tantalum silicate glasses is quantitatively determined based on the structure of the nearest neighbor congruent compound through the lever rule. These findings offer a precise prediction of tantalum silicate glass properties with quantitative control over local structural environment of the disordered materials.     

Tantalum (oxy)nitrides prepared using reactive sputtering for new nonplatinum cathodes of polymer electrolyte fuel cell

Tantalum (oxy)nitrides (TaO_xN_y) have been investigated as new cathodes for polymer electrolyte fuel cells without platinum. TaO_xN_y films were prepared using a radio frequency magnetron sputtering under Ar + O₂ + N₂ atmosphere at substrate temperatures from 50 to 800 °C. The effect of the substrate temperature on the catalytic activity for the oxygen reduction reaction (ORR) and properties of the TaO_xN_y films were examined. The catalytic activity of the TaO_xN_y for the ORR increased with the increasing substrate temperature. The ORR current density at 0.4 V vs. RHE on TaO_xN_y prepared at 800 °C was approximately 20 times larger than that on TaO_xN_y prepared at 50 °C. The onset potential of the TaO_xN_y for the ORR was obtained at the ORR current density of −0.2 μA cm⁻². The onset potential of the TaO_xN_y prepared at 800 °C was ca. 0.75 V vs. RHE. The X-ray diffraction patterns revealed that Ta₃N₅ structure grew as the substrate temperature increased. While, the ionization potentials of all specimens were lower than that of Ta₃N₅, and decreased with the increasing substrate temperature. The TaO_xN_y which had Ta₃N₅ structure and lower ionization potential might have a definite catalytic activity for the ORR.     

Second harmonic generation in germanotellurite bulk glass‐ceramics

In this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100?x) [70TeO₂–10GeO₂–10Nb₂O₅–10K₂O]–xAg₂O (x=0‐6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X‐ray diffraction, UV‐Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb_1/3Te_2/3]₂O_4.8, which has been investigated for its second‐order optical activity. Transparent to translucent glass‐ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass‐ceramic samples as a function of their synthesis procedure. It is suggested that the second‐order optical properties observed are strongly related to the organization of crystallites within phase‐separated domains.     

Synthesis and thermoelectric performance of Ta doped Sr0.9La0.1TiO3 ceramics

Ceramics samples of Sr_0.9La_0.1Ti_1−xTa_xO₃ have been synthesized by conventional solid-state reaction method. X-ray powder diffraction characterization indicates that all samples are of single phase with cubic symmetry. The high-temperature electrical resistivity decreases with the increasing of tantalum content except for x = 0.05 sample. Negative Seebeck coefficients have been obtained for all samples, which means conduction mechanism being n-type. The absolute Seebeck coefficient decreases with the increase of tantalum concentration. The power factor decreases with increasing of tantalum substitution. Small amount tantalum doping can reduce the thermal conductivity. The lowest thermal conductivity obtained is 2.9 W/mK for x = 0.03 at 1074 K. The highest thermoelectric figure of merit still observes in Sr_0.9La_0.1TiO₃, reaches 0.29 at 1046 K, which is a relatively higher value in n-type oxide thermoelectric materials.     

Influences of annealing temperature on anti-reflective performance of amorphous Ta2O5 thin films

Influences of thermal annealing on structural, optical and morphological properties of the tantalum pentoxide (Ta₂O₅) thin films were investigated and anti-reflective performances were discussed in detail. The Ta₂O₅ thin films were deposited onto Corning Glass (CG), Si, GaAs and Ge substrates by radio-frequency (RF) magnetron sputtering technique using Ta₂O₅ ceramic target. The obtained secondary ion mass spectroscopy (SIMS) analysis results showed that uniform Ta and O distribution have formed throughout depth of the films deposited on substrates. The X-Ray diffraction (XRD) results indicated that the annealed Ta₂O₅ thin films at 100, 200, 300 and 500?°C have exhibited amorphous (a-Ta₂O₅) characteristic. The increased temperature has resulted in increasing the surface roughness from 0.67 to 1.60?nm. The optical transmittance of the annealed thin films has increased from 70.85 to 80.32% with increasing temperature. Spectroscopic ellipsometer (SE) measurement results demonstrated that the increased temperature has increased the refractive index of the Ta₂O₅ thin film from 2.11 to 2.18. The Ta₂O₅ thin film has reduced the average optical reflectivity of the Si, GaAs and Ge substrates by 78, 55 and 70%, respectively. In addition, thermal annealing process has decreased the optical reflectivity of the film. The obtained experimental results showed that single-layer Ta₂O₅ thin films can be used as anti-reflective layer in optical and optoelectronic applications. The best optical transmittance and anti-reflective performance were obtained at the annealing temperature of 500?°C.     

Bioactive glass-ceramics prepared by powder sintering and crystallization of polyphosphate glass containing strontium

Melt-quenching method was employed for obtaining a glass-ceramic with the following composition 42P₂O₅·40CaO·5SrO·10Na₂O·3TiO₂ (mol%) glass. The crystallization and sintering behavior of glass have been studied by using DTA, HSM, XRD, FTIR and SEM methods. It was determined that the surface and volume crystallization mechanisms act simultaneously in bulk glass samples. The comparison of DTA and HSM data revealed that the sintering and crystallization processes are independent. The sintered calcium phosphate glass-ceramic which contained bioactive β-Ca₃(PO₄)₂ and β-Ca₂P₂O₇ phases was successfully prepared. It was determined that during crystallization the primary phase in the precipitate was β-Ca(PO₃)_2. Other phases appearing in the resulting glass-ceramic were: α-Ca₂P₂O₇, γ-Ca₂P₂O₇, Ca₄P₆O₁₉ and CaHPO₄(H₂O)₂. Crystalline phases containing Sr and Ti were not detected. SEM analysis of the glass-ceramic microstructure revealed surface crystallization of glass particles and plate-like morphology of crystal growth. The result of the in vitro bioactivity showed that no apatite layer was formed on the surface of the as-prepared glass-ceramic samples after immersion in the simulated body fluid (SBF).     

Thermal expansion of specimens of niobium and tantalum pentoxides obtained by melting in an optical furnace

Thermal expansion of high-purity niobium and tantalum pentoxides is studied. It is shown that specimens of Nb₂O₅ and Ta₂O₅ obtained by melting in an optical furnace and subsequent rapid cooling in air to room temperature possess a domain of negative thermal expansion and hysteresis of the dependence of the elongation on the temperatures of heating and cooling. Since the volume of a test cell computed from data of x-ray measurement increases with growth in the temperature, the negative values of the elongation of specimens of melted Nb₂O₅ and Ta₂O₅ can be explained by merging of microcracks formed due to anisotropy of the thermal expansion when the ingots are cooled. When designing and fabricating ceramic articles with protective coatings from niobium and titanium pentoxides to be used at 1000°C, preference should be given to ceramics with low and even negative values of CLTE. __________ Translated from Novye Ogneupory, No. 4, pp. 38–43, April, 2007.     

Effect of Ta2O5 addition on the structure,crystallization mechanism,and properties of CaO–B2O3–SiO2 glasses for LTCC applications

CaO–B₂O₃–SiO₂–Ta₂O₅ (CBST) glass-ceramics, with different Ta₂O₅ content, (up to 6 mol%), have been prepared by using glass melt quenching followed by heat treatment between 800 and 880 °C. The Fourier Transform Infrared (FTIR) results showed that the stronger the attraction of Ta⁵⁺ to the oxygens in the BO₃^3? and SiO₃^2? structures, the more easily the B–O and Si–O bonds will be destroyed. The underlying reason is most probably the high field strength of Ta⁵⁺, which results in a weakening of the vibration intensities of the [BO₃] and [SiO₄] units. Moreover, the Differential Scanning Calorimetry (DSC) results showed that the softening point (T_g), crystallization starting temperature (T_c1), and exothermic crystallization peak temperature (T_p1), of the CaSiO₃ phase, shifted to higher values with the addition of Ta₂O₅. Also, the crystallization activation energy (E_a) and the glass stability factor (ΔT) of the CaSiO₃ phase increased, which indicated that the CaSiO₃ phase of the glass became inhibited by the addition of Ta₂O_5. It was, thus, obvious that there was a need of glass characterization. The results of the crystallization kinetics showed that the critical cooling rate decreased with the addition of Ta₂O₅, which indicated that the viscosity of the system had increased. The CBST glass-ceramics, containing 1 mol% Ta₂O_5, that were sintered at 875 °C for 15 min showed excellent dielectric properties: ε_r = 6.22 and tanδ = 1.19 × 10^?3 (1 MHz). To sum up, CaO–B₂O₃–SiO₂–Ta₂O₅ glass-ceramics are potential low temperature co-fired ceramic substrate materials.     

Long-term degradation of Ta2O5-doped Bi2O3 systems

Bismuth oxide in δ-phase is a well-known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). 5-10 mol% Ta₂O₅ are doped into Bi₂O₃ to stabilize δ-phase by solid state reaction process. One Bi₂O₃ sample (7.5TSB) was stabilized by 7.5 mol% Ta₂O₅ and exhibited single phase δ-Bi₂O₃-like (type I) phase. Thermo-mechanical analyzer (TMA), X-ray diffractometry (XRD), AC impedance and high-resolution transmission electron microscopy (HRTEM) were used to characterize the properties. The results showed that holding at 800-850 °C for 1 h was the appropriate sintering conditions to get dense samples. Obvious conductivity degradation phenomenon was obtained by 1000 h long-term treatment at 650 °C due to the formation of α-Bi₂O₃ phase and Bi₃TaO₇, and 〈1 1 1〉 vacancy ordering in Bi₃TaO₇ structure.     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.