Tetragonal Phase Content Research Articles

Study of the structural and phase state of ceramics synthesized from 6YSZ - Al2O3 – HfO2 by semi–dry pressing followed by sintering in vacuum

The study investigates the properties of 6YSZ – Al2O3 – HfO2 powder mixture and the resulting ceramics obtained by semi-dry pressing followed by sintering in vacuum. X-ray fluorescence spectrometry revealed the primary constituents as zirconium (81%), aluminum (8.7%), yttrium (5.7%), and hafnium (3.5%). The average particle diameter was 0.5 μm, with specific surface area and bulk weight recorded at 18,535 cm2/g and 0.84 g/cm3, respectively. X-ray phase analysis indicated a predominance of monoclinic zirconium dioxide. Sintering at 1400-1600°C transformed the phase composition, enhancing density and microhardness, with values peaking at 5.8 g/cm3 and 12.1 GPa at 1600°C. This process also increased the tetragonal phase content to 63%. The ceramics exhibited the highest crack resistance at 1600°C, attributed to the stabilized tetragonal zirconium dioxide. Microstructural analysis confirmed the homogenous distribution of the elements and the presence of fine fractions influencing microstructural properties. 1600°C was found to be the optimal temperature for sintering the 6YSZ – Al2O3 – HfO2 ceramics.

In Vitro Evaluation of Speed Sintering and Glazing Effects on the Flexural Strength and Microstructure of Highly Translucent Multilayered 5 mol% Yttria-Stabilized Zirconia.

This study aimed to investigate the impact of speed sintering and glazing on the flexural strength and microstructure of multilayered 5 mol% yttria-stabilized (5Y-) zirconia, which remains unknown. Bar-shaped specimens (N = 600) were fabricated from 5Y-zirconia (FX; Ceramill Zolid FX ML, ST; Katana STML) by cutting, polishing, sintering (conventional and speed sintering), and then glazing. A flexural strength test (n = 30/group), field emission scanning electron microscopy (FE-SEM) observation (n = 2/group), and an X-ray diffraction (XRD) study with Rietveld refinement (n = 1/group) were performed. The flexural strength was analyzed using three-way ANOVA and a post hoc Scheffé test. The grain size was analyzed using the Kruskal-Wallis H test and Bonferroni-Dunn post hoc test. Flexural strength slightly decreased in the nonglazed FX after speed sintering (p < 0.05). Glazing with and without glazing paste did not affect flexural strength at both sintering speeds (p > 0.05). Speed sintering and glazing minimally changed the Weibull modulus and phase fraction, and did not affect grain size (p > 0.05). ST had a larger grain size and lower tetragonal phase content than FX and had a lower flexural strength than FX in most groups (p < 0.05). Overall, the multilayered 5Y-zirconia is considered suitable for dental application using speed sintering and glazing.

Efficient visible light photodegradation of BiVO4:Yb3+/Tm3+ with high content of tetragonal phase

Efficient visible light photodegradation of BiVO4:Yb3+/Tm3+ with high content of tetragonal phase

The phase-stabilized behavior of Sc2O3–Y2O3 co-doped ZrO2 nanopowders by co-precipitation synthesis

Single stabilizer-doped ZrO2 has drawbacks such as inferior mechanical properties and thermal stability, making it difficult to obtain ZrO2 ceramics with good density and high crystallinity. Thus, it is expected that ZrO2 is doped and modified by two or more stabilizers. In this paper, the Sc2O3–Y2O3–ZrO2 nanocomposite ceramic powders were prepared using ZrOCl2⋅8H2O, ScCl3⋅6H2O, and YCl3⋅6H2O as raw materials and polyvinylpyrrolidone as dispersant. They calcined at diverse temperaturesby the pressureless sintering-assisted co-precipitation method after being pressed into disc shape. Sc2O3 and Y2O3 were added as ZrO2 stabilizers to ameliorate the lack of insufficient mechanical properties and high-temperature stability of ZrO2 ceramics caused by single doping. To study the stability of the phases at high temperatures, the specimens were characterized by TG-DTG, XRD, Raman, SEM, FT-IR, etc. The effects of different pH valuesand different calcination temperatures on the Sc2O3–Y2O3–ZrO2 nanocomposite ceramics were investigated. It was demonstrated that ternary doping has very excellent phase stability. After calcination no monoclinic phase appeared, and the precursor samples were transformed from amorphous to a large amount of tetragonal phases and a few cubic phases. The samples at pH = 10 and calcination temperature of 1000 °C showed the best stabilization, the most uniform grain development, the best crystallinity, the most regular morphology, the highest tetragonal phase content of 89.2 %, the stabilization rate of 94.58 %, and the highest relative density of 98.75 %. The results show that this nanocrystalline powder can be used to prepare high-density nanoceramics. Furthermore, the activation energy for grain growth of Sc2O3–Y2O3–ZrO2 nanocomposite ceramics was calculated as 13.87 kJ/mol. This paper provides a theoretical and experimental research basis for the controlled synthesis of Sc2O3–Y2O3–ZrO2 nanocomposite ceramics using a pressureless sintering-assisted co-precipitation method.

Preparation of La doped BiVO4 under weak acid environment to enhance (040) crystal plane exposure and photocatalytic activity: characterization and degradation mechanism

In this paper, a 0.0%-5-BVO sample with (040) crystal plane exposure was successfully prepared by a hydrothermal method in a pure aqueous-phase environment free of organic solvents by modulating the pH of the precursor solution, and its I040/I-121 reached 1.70, which is 6.8 times that of the standard PDF#14–0688. Subsequently, a 4.0%-5-BVO sample was prepared by using La(NO3)3–6H2O as the La source to further promote the (040) crystal plane exposure via La. The I040/I-121 of the 4.0%-5-BVO sample reached 3.05, which was 12.2 times that of the standard PDF#14–0688, and exhibited stronger photocatalytic activity compared with that of the 0.0%-5-BVO. In addition, a correlation between precursor solution pH and the crystalline phase of BiVO4 was observed, with increasing pH and decreasing sample I-121/I200 from 4.32 for 4.0%-3-BVO to 0.34 for 4.0%-9-BVO, with decreasing monoclinic and increasing tetragonal phase content. La also had an effect on the crystalline phase, causing I-121/I200 to decrease from pre-doped 8.85 before doping to 2.70 after doping, contributing to the change of BiVO4 toward the tetragonal phase.

Non-hydrolytic sol-gel synthesis of BaTiO3 nano-powder: Effect of calcination temperature and modified titanium source on particles

In this study, BaTiO3 nanopowders were prepared by non-hydrolytic sol-gel (NHSG) method using barium acetate and tetrabutyl titanate (TBT) as precursors and acetylacetone (Hacac) as additive. The effects of acetylacetone modification and calcination temperature on nanoparticle size and crystalline phase were evaluated. The products were analysed by SEM, TEM, DSC/TG, FTIR, XRD, Raman. FTIR analysis showed the formation of Ba-O-Ti bond at the sol stage of the NHSG method. DSC/TG and XRD analyses showed that BaTiO3 was produced at 500 ℃. According to SEM/TEM, the particle size of the powder becomes larger as the temperature increases, meanwhile the addition of acetylacetone can make the final product particle size decrease. Raman analysis showed that BaTiO3 has the presence of tetragonal phase, so the crystalline phases of the product and impurities were analysed by XRD refinement, and the results showed that the relative content of tetragonal phase of BaTiO3 was linearly correlated with the calcination temperature.

Controllable preparation of high tetragonal phase BaTiO3 nano/microstructure and its boosting piezocatalytic properties

BaTiO3 terrace-like nano/microstructure were synthesized via a facile solvothermal method without surfacatant or template by controlling pH value. The phase structure, morphology and properties of the samples were characterized by XRD, FT-IR, XPS, SEM, UV–vis and ESR spectrum, etc. The piezoelectric potential analysis are calculated by finite element method simulation for BaTiO3 prepared at different pH values under ultrasonic vibration. Morphology and crystal phase transform mechanism of BaTiO3 at different pH values are proposed, respectively. The results show that pH value has a significant effect on the phase, crystallinity, morphology, size and piezocatalytic performance of BaTiO3. When pH value is 10, BaTiO3 exhibits spherical shape with an average size of ∼200 nm. With the increase of pH value, the morphology transforms grape-like shape from terrace-like shape. The transformation mechanism for BaTiO3 is proposed to be a two–step growth model: initial nucleation and ripen, an oriented attachement accompanied by Ostwald ripening. H+ ions in OH− group occupy the Ba2+ position and affect the supersaturation of Ti (OH)62−, thereby blocking the migration channel of Ba2+ and changing the crystal symmetry, resulting in changes in the content of tetragonal phase. FEM simulated shows the electric potential of BaTiO3 is dominated by their morphologies. Compared with other samples, the best piezocatalytic performance of BaTiO3 terrace-like nano/microstructure is demonstrated at pH = 12, which is the rate constant k of 15.5 × 10−3 min−1 by degrading 93 % of RhB dye solution in 180min, and keep almost unchanged after five cycles. The attractive piezocatalytic properties are considered to benefit from BaTiO3 terrace-like nano/microstructure, which is composed of the numerous nanounits self-assembly micrometer-scale structure.

Phase structure, domain structure, thermal stability, and high-temperature piezoelectric response of BiFeO3–BaTiO3 lead-free piezoelectric ceramics

High-temperature lead-free piezoceramics with a large piezoelectric constant d33 and a high depolarization temperature Td have long been a target of ferroelectric researchers. In this work, (1-x)BiFeO3-xBaTiO3 ceramics with MnO2 and Li2CO3 additives (BF-xBT) were fabricated with traditional ceramic preparation technology. The best piezoelectric ferroelectric properties and thermal stability d33 = 185 pC/N, Pr = 33.152 μC/cm2, Tc = 470 °C, and Td = 460 °C were obtained for x = 0.32. The tetragonal (T) phase content of BF-xBT ceramics increases gradually with an increase of BT content, and the temperature stability improves. In particular, an in-situ d33 test indicates that BF-xBT ceramics have large piezoceramics coefficients with d33 = 450.5 pC/N at a temperature of T = 334 °C. Piezo force microscopy and transmission electron microscopy tests show that nanodomains and polar nanoregions play a key role in the improvement of piezoelectric response. BF-xBT ceramics appear to be the most promising candidates to replace PZT ceramics in high-temperature applications.

Enhanced catalytic activity of Molar-like BaTiO3 by oxygen vacancies

Oxygen vacancies are found to have significant effects on the piezo-photocatalytic performance. For this reason, Molar-like and Bamboo-like BaTiO3 with the same tetragonal phase are synthesized by a two-step hydrothermal method. Molar-like BaTiO3 exhibits a superior piezo-photocatalytic performance by degrading the organic dye indigo carmine (IC), whose kinetic constant of 0.099 min−1 is 1.80 times higher than that of Bamboo-like BaTiO3. The same conclusion is drawn while the differences in specific surface areas are eliminated. There are more oxygen vacancies in Molar-like BaTiO3 compared to Bamboo-like BaTiO3, as shown in XPS results. The oxygen vacancies are favorable for light adsorption and O2 activation, thus an excellent photocatalytic performance is achieved. XRD refinements show that Molar-like BaTiO3 has a slightly higher content of piezoelectric tetragonal phase and stronger lattice distortion than Bamboo-like BaTiO3. However, the piezoelectric polarization of Molar-like BaTiO3 is weakened and the number of effective carriers is reduced due to more oxygen vacancies. The presented work provides a profound reference for the structural design of catalysts.

A comparative investigation on micro-channel by using direct laser ablation and liquid-assisted laser ablation on zirconia

In this work, direct laser ablation (DLA), liquid-assisted laser ablation in water (LALA-W) and in ethanol (LALA-E) is applied to fabricate single micro-channels on the zirconia ceramic by using a picosecond laser. To assess the machining ability of them, micro-channels fabricated are characterized and compared the differences in morphology, geometric profile, chemical and phase composition. The morphological results indicate that both LALA-E and DLA can fabricate microchannel with obvious recast layer and cracks, and LALA-W can fabricate microchannel with a porous surface, and almost no recast layer and cracks. The results of geometric characteristics show that LALA-W can fabricated micro-channels with “U” shape profile with 52.74% enhancement in depth compared to that “V” shape by DLA and LALA-E. The XPS results demonstrate that LALA-W can exhibit the smallest oxygen vacancies with 50.01% than that of LDA 53.81% and LALA-E 54.56%. For XRD results, after machining by all three processes, the zirconia ceramic undergoes the tetragonal→monoclinic phase transformation, resulting in an increase in monoclinic phase. While LALA-W exhibits the smallest increase in monoclinic phase from 9.9% to 12.7%, and has the most tetragonal phase content of 58.8%.

Effect of superspeed sintering on translucency, opalescence, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized tetragonal zirconia polycrystal and 6 mol% yttria-stabilized partially stabilized zirconia ceramics

Statement of problemThe optical properties of recently developed multilayer zirconia have mainly been studied for the effects of conventional sintering and speed sintering but not as much for the effect of superspeed sintering. As superspeed sintering protocols typically require a higher sintering temperature and higher heating and cooling rates than speed- and conventional sintering protocols, the optical properties of superspeed sintered zirconia may be affected differently. PurposeThe purpose of this in vitro study was to investigate the effect of superspeed sintering on the optical properties, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized (4Y-) and 6 mol% yttria-stabilized (6Y-) zirconia. Material and methodsMultilayered 4Y- and 6Y-zirconia were sectioned. After conventional and superspeed sintering, the translucency parameter (TP), and opalescence parameter (OP) were measured with a spectrophotometer (n=10). To obtain the grain sizes from the field emission scanning electron microscopy (FE-SEM) images for each layer (n=2), more than 500 (6Y-zirconia) and 800 grains (4Y-zirconia) were measured by linear intercept methods. The phase fractions were obtained through X-ray diffraction (XRD) analysis by using the Rietveld method (n=1). The results were analyzed by 3-way ANOVA and post hoc Tukey honest significant difference tests (TP and OP) and by 3-way ANOVA and post hoc Scheffé tests (grain size) (α=.05). ResultsNo layers exhibited a significant difference in TP after superspeed sintering, except the dentin layer (DL) and transition layer 2 (T2) of 4Y- and 6Y-zirconia, respectively. The TP increased (P<.05) in DL for superspeed sintered 4Y-zirconia and decreased (P<.05) in T2 for the superspeed sintered 6Y-zirconia. However, the difference in TP by superspeed sintering was lower than the perceptibility thresholds of 50:50%. The OP decreased (P<.05) in the DL and T2 of 4Y-zirconia after superspeed sintering. For 6Y-zirconia, the OP decreased (P<.05) in all layers except for the transition layer 1 (T1) after superspeed sintering. However, the difference in OP values was minimal, with only a 1.1 difference observed for Zolid Gen-X (4Y) and a range of 1.22 to 1.62 for Katana UTML (6Y) when using superspeed sintering. No significant change was found in the grain size after superspeed sintering of either zirconia. Regardless of the sintering speed, the average grain size of the 6Y-zirconia (conventional: 2.09 to 2.21 μm; superspeed: 2.11 to 2.20 μm) was larger than that of the 4Y-zirconia (conventional: 0.50 to 0.52 μm; superspeed: 0.52 to 0.54 μm). Owing to superspeed sintering, the metastable tetragonal (T′) phase content increased while the tetragonal (T) phase decreased in 4Y-zirconia; in 6Y-zirconia, the cubic (C) phase content increased, while the T′-phase content decreased. ConclusionsSuperspeed sintering did not result in any clinically significant changes in the translucency and opalescence of 4Y- or 6Y-zirconia.

Research on the tetragonal phase content and microstructure of microwave-assisted sintering Y-PSZ system doped Bi2O3

Partially stabilized Y2O3–ZrO2 (Y-PSZ) is often used as a material in the field of oxygen sensors and batteries. However, the presence of a tetragonal phase will seriously reduce the conductivity of Y-PSZ materials. As a sintering aid, Bi2O3 can be used to sinter materials with high oxygen ion conductivity at low temperatures. It is the first choice for the Y-PSZ doped system. A new microwave sintering technique prepared Bi2O3–Y-PSZ powders. The effects of doping amount of Bi2O3 on the microstructure, phase transition, and tetragonal phase content of Y-PSZ during sintering were researched. The results displayed that doping Bi2O3 improved the tetragonal phase content of the ZrO2. The tetragonal phase content of the samples increased from 59.72% to 94.69% after sintering at 750 °C for 1 h. After doping Bi2O3, the aggregation of the samples reduced gradually, and the particles dispersed evenly. The average particle sizes of raw material and samples doped with different amounts of Bi2O3 were 0.0794 μm, 0.0638 μm, 0.0629 μm, 0.0794 μm, 0.1116 μm, respectively. Therefore, in the doping amount (1 mol%-4 mol%), the Bi2O3 doped Y-PSZ system with 2 mol% has the highest tetragonal phase content, the best dispersion, the smallest average particle size, and the most uniform particle distribution.

A detailed investigation of the structural stability, ionic conductivity and in situ δ-phase formation of YxBi2xO3

The in situ δ-phase formation for a series of yttrium-doped Bi2O3 materials was studied by Raman spectroscopy and high resolution X-ray diffraction under variable temperature conditions. Contrary to previous reports, for dopant concentrations less than 25%, the cubic ô-phase was not fully stabilized at room temperature - tetragonal phase content was evident in both Raman spectra and powder diffractograms. Arrhenius plots also showed evidence of a phase transformation by the distinct large step change in conductivity in the temperature region where the tetragonal-cubic phase transformation was noted. Both the thermal expansion and ionic conductivity of the cubic phase decreased with increasing dopant content.

Effect of sintering time on the microstructure and stability of Al2O3–ZrO2 composite powders under microwave-assisted sintering

The function of ceramic coating is closely related to the construction technology and the quality of ceramic powders. Generally, Al2O3–ZrO2 powders are rapidly sprayed on the material surface at high temperatures to obtain better performance. Improving the quality of Al2O3–ZrO2 powders can make them more widely used in ceramic coating. In this paper, microwave sintering was used to enhance the sintering process of the powders, and the effect of sintering time on the microstructure, properties, and stability of Al2O3–ZrO2 powders was investigated. The results proved that microwave heating could improve the crystallinity and stability of the samples. At 900 °C, the tetragonal phase content in samples with different sintering times were 63.05%, 63.25%, 62.39%, and 63.22%, respectively. The average particle sizes obtained by Gaussian fitting are 1.04 μm, 0.83 μm, 0.88 μm, 0.86 μm, respectively. The Gaussian fitting particle size data was consistent with the normal distribution. Compared with the particle size of raw material (1.10 μm), the particles were refined, and the dispersion effect was noticeable. Therefore, the best sintering time for microwave sintering Al2O3 stabilized zirconia was 2 h. This paper aims to provide reasonable data support for improving the preparation of high-quality Al2O3-PSZ ceramic powders and to guide the industrial production of Al2O3-PSZ powders.

Tuning of phase content, microstructure and thermal expansion of MgPSZ

MgO partially stabilized zirconia (xMgPSZ, with x = 3–14 mol% MgO) was prepared by a ceramic route, starting from pure metal oxides. 7.5MgPSZ, the focus of this work, was sintered at 1700 °C and cooled at various rates (1, 2 or 4 °C/min), without or with 1 or 2 intermediate dwells (1400, 1300, and 1000 °C), and dwell durations (1–6 h). Customized thermal expansion (TE) data analysis is used to estimate the monoclinic (M) phase content (with discrimination between large and small particles), while powder X-ray diffraction (XRD) provides an accurate cubic (C) phase assessment. With the tetragonal (T) phase content determined from balance to 100%, detailed sets of structural (M, C, T) and microstructural information (M particle size), are grouped in novel radar-type charts. Original benchmarking exercises using literature data on up thermal shock resistance and the characteristics of a commercial MgPSZ, provide unique insights on the thermal performance of these materials, and property tuning rationale.

Large piezoelectricity in BiScO3-PbTiO3 based perovskite ceramics for high-temperature energy harvesting

Advanced high-temperature piezoceramic energy harvesters (HT-PEHs) highly rely on perovskite ceramics with large high-temperature piezoelectricity. However, it remains a great challenge to achieve high piezoelectric coefficient (d33) at elevated temperatures, which severely limits the development of piezoelectric materials in cutting-edge energy harvesting applications. Here, yBiScO3-xPbTiO3-0.05Pb(Zn1/3Nb2/3)O3 (yBS-xPT-PZN) ternary perovskite piezoceramics are prepared, in which the morphotropic phase boundary (MPB) composition (x/y = 0.60/0.35) exhibits a large d33 of 655 pC/N at 300 °C, outperforming many reported other perovskite piezoceramics. The excellent high-temperature piezoelectricity should benefit from the lattice softening effect and the stable ferroelectric domain state associated with the high tetragonal phase content. In addition, the HT-PEH assembled from the MPB sample exhibits good power generation performance (e.g., a giant power density of 418 μW/cm3) at 300 °C, and can charge a 10 μF commercial capacitor to 7 V within 40 s. Such a large piezoelectric coefficient and power density of yBS-xPT-PZN system at a high temperature of 300 °C is a promising candidate for fabricating high-performance HT-PEHs to meet the urgent requirements of advanced high-temperature energy harvesting applications.

Excellent temperature stability of energy storage performance by weak dipolar interaction strategy

High-performance dielectric materials are widely used in energy storage applications, and temperature stability at extreme conditions is rarely considered yet. In this work, the Bi0.5Na0.5TiO3–Sr0.7Bi0.2□0.1TiO3–xNaNbO3 (x = 0, 0.05, and 0.15) system is designed with a room-temperature ergodic relaxor character to explore energy storage evolution with temperature. The addition of NaNbO3 increases tetragonal (P4bm) phase content and relaxor disorders and leads to a downshift of transition temperature, as verified by Rietveld refinement, dielectric analysis, and in situ Raman spectra. Superior temperature stability of recoverable energy storage density (WRec, change rate: δ ≤ 14%) and efficiency (η = 0.79–0.98) is found in x = 0.15 composition in a wide temperature range of 243–373 K, in contrast to a significant variation for x = 0 (δ ≤ 85%, η = 0.08–0.88) and 0.05 (δ ≤ 36%, η = 0.60–0.96) compositions. The dielectric relaxation speed is faster in x = 0.15, as characterized by on–off-electric field dielectric curves. This work demonstrates that the weak-dipolar-interaction system retards dipolar coalescence under cryogenic temperature and, thus, maintains high energy storage efficiency, which predicts their suitability in energy storage applications at an extreme condition.

Blackening Mechanism and Mechanical Properties Variation of Zirconia Ceramic Induced by Active Metal Brazing

Blackening of zirconia (ZrO2) ceramics often occurs in active metal brazing, however, its discoloration mechanism and induced variation in mechanical properties remain unclear. Herein, ZrO2 ceramic and Ti are successfully brazed by Ag–Cu–Pd filler in vacuum along with the blackening phenomenon. In the brazed joints, the reaction layers of TiO2 + Ti3(Cu, Pd)O are formed adjacent to ZrO2, indicating that partial oxygen in ZrO2 is taken by active Ti in the liquid filler that dissolved from the Ti substrate. Furthermore, the height of the blackened ZrO2 ceramic near the brazing seam is in line with the amount of Ti content added to the filler, which infers that bulk‐sized black ZrO2 can be efficiently obtained by the interfacial reaction between Ti and ZrO2. Additionally, the black ZrO2 is having abundant Zr3+ defects and more tetragonal phase content than the original ZrO2. The formation of Zr3+ defects results in the blackening of ZrO2, while the phase transformation leads to reduced hardness, improved impact toughness, and enhanced wear resistance of black ZrO2. Thus, this blackening phenomenon of ZrO2 ceramics provides a new way to tune the mechanical properties of ZrO2.

Crystal structure and morphology of CeO2 doped stabilized zirconia ceramics under high-frequency microwave field sintering

Under high-frequency microwave irradiation, zirconia ceramics were prepared by sintering nano-CeO2 (Ce = 7 mol%) doped zirconia powder. The different effects of temperature environment on the phase structure transformation, surface functional groups, microstructure, growth process, and density of doped zirconia were analyzed, and the optimized microwave sintering process for zirconia was determined. The experimental results reveal that the tetragonal phase of zirconia is positively correlated with the temperature when the temperature reaches about 1100 °C in the studied range. The reason is that the grain grows with the increase of sintering temperature, and the surface energy of grain decreases, which leads to the fluctuation of tetragonal phase content. The density of zirconia reaches 98.03% at 1300 °C, and the growth activation energy is 27.40 kJ/mol. There is no abnormal growth of zirconia particles, and the phase transition temperature decreases, which is attributed to the efficient heating of microwave and the incorporation of nano-ceria stabilizer.

Strong Eu3+ luminescence in Lа1-x-yErx/2Eux/2CayVO4 nanocrystals: The result of co-doping optimization

Co-doped with Ca2+ and Er3+ ions LаVO4:Eu crystalline nanoparticles are synthesized and investigated with a goal to clarify the mechanisms of Ca2+ and Er3+ impurities effects on Eu3+ ions luminescence and to find compositions with enhanced luminescence intensity. The XRD analysis reveals dependence of crystal structure on dopants concentration: monoclinic crystal phase is observed for low dopant concentrations and content of tetragonal crystal phase increases with dopant concentrations increase. The SEM investigation reveals formation of nanoparticles with two types of shapes. Photoluminescence spectra consist of lines caused by f-f transitions in the Er3+ and Eu3+ ions. It has been shown that dependence of the Eu3+ ions luminescence intensity on the Er3+ and Ca2+ concentrations is caused by cumulative effects of dopants on crystal lattice structure, on defects in the first coordination sphere of the Eu3+ ions and on efficiency of excitation energy transfer. The maximal luminescence intensity is found for the Lа0.8Er0.05Eu0.05Ca0·1VO4 composition. The corresponded intensity is as much as 19 ± 2 and 8 ± 2 times higher than luminescence intensity of the Lа0.95Eu0.05VO4 and Lа0.9Eu0.05Ca0·05VO4 compounds, respectively. Conclusion is made that Er3+ and Ca2+ ions co-doping is a promising way to increase luminescence efficiency of the Eu3+ ions in the LaVO4 nanocrystals.