Zircon Structure Research Articles

Temperature-induced phase transitions and structural features of non-polar phases stabilizing below TC in the PbZrO3–LaMg2/3Nb1/3O3 system

Lead zirconate-lanthanum magnesium niobate (Pb(1- x )La х [Zr(1- x )Mg2 х /3Nb х /3]O3) solid solutions with x up to 10 mol.% have been obtained by solid phase synthesis method. It has been found that solid solutions with up to ∼6.0 ÷ 7.0 at.% La3+ have the rhombic structure of lead zirconate at the room temperature, but at 0.01 ≤ х ≤ 0.04, it is preceded by an intermediate antiferroelectric phase. It is structurally similar to those found previously in the lead zirconate-stannate system and in lead hafnate. At large values of x , the superstructure is lost in nonpolar phases and the long-wavelength modulation becomes incommensurate.

Effect of different surface treatment modalities on crystal structure and biaxial flexural strength of super translucent zirconia.

Objectives: To study the outcome of different surface treatments on X ray diffraction analysis (XRD) and flexural strength of super translucent zirconia. Materials and Methods: Forty identical discs were milled from presintered super translucent zirconia blank (VITA YZ ST, VITA Zahnfabrik, Germany). Specimens were classified into 4 groups according to the surface treatment used: Group C: no treatment (control group), Group S: discs were airborne particle, Group P: discs were treated with primer and Group SP: discs were airborne particle then, they were treated with primer. All specimens were subjected to XRD analysis and biaxial flexural strength test. Results: The highest biaxial flexural strength recorded value was for the C group (462.11±17.33 MPa) while the lowest one was recorded for S group (310.33±7.78 MPa). Applying one way ANOVA and Tukey test revealed a statistically significant difference among all tested groups. The XRD analysis of specimens that were treated with different surface treatments revealed the evolution of monoclinic phase transformation in groups S and SP. Conclusions: The airborne particle abrasion resulted in the evolution of tetragonal to monoclinic phase transformation on the zirconia surface which in turn negatively affected the flexural strength of super translucent zirconia.

A comparative study of structural, thermal, and optoelectronic properties between zircon and scheelite type structures in SrMoO4 compound: An ab-initio study

First principles calculations were carried out on the SrMoO4 compound which has been of interest owing to its technologically important physical properties. The structural, electronic, optical and thermal properties of this compound have been investigated under low pressure (LP) through the full potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory. It is found that the phase transition from zircon to scheelite type structure occurs at negative pressure. The calculated ground state properties in scheelite structure are found to be in good accord with previously published data. Using the recently developed Tran Blaha-modified Becke Johnson approach, we have also studied the electronic band structure of this compound which shows the semiconducting behavior with a direct band gap of 4.30 eV in the scheelite phase, whereas the band gap is found to be 2.18 eV in the zircon phase. Various thermodynamic properties including the thermal volume expansion coefficient and heat capacities at constant volumes and pressures were calculated via the quasi-harmonic Debye model at different temperatures (0–1000 K). Furthermore, optical properties such as complex dielectric function, refractive index, and reflectivity spectra of the titled compound were studied for incident electromagnetic waves in an energy range up to 16 eV. The contributions to various transitions peaks in the optical spectra are analyzed and discussed with the help from the energy dependent imaginary part of the dielectric function.

Effect of the ionic radius of stabilizing oxide cation on the local structure and transport properties of zirconia based solid solutions

Abstract Features of the local structure of ZrO2-Yb2O3, ZrO2-Y2O3-Yb2O3 and ZrO2-Sc2O3-Yb2O3 single crystals have been studied using optical spectroscopy. The probability of oxygen vacancies to occupy the first coordination shells of the Sc3+, Yb3+ and Y3+ stabilizing oxide cations has been shown to vary in the test solid solutions. Furthermore it has been shown that the probability of oxygen vacancies to occupy the first coordination shells of the Sc3+ ions is higher than their probability to occupy the first coordination shells of the Yb3+ and Y3+ ions. It has been shown that the transport properties of the ZrO2-Sc2O3-Yb2O3 and ZrO2-Y2O3-Yb2O3 solid solutions depend significantly on the ionic radii of the stabilizing oxide cations located in the first coordination shells of oxygen vacancies. For cations with small ionic radii (Sc3+, Yb3+) the height of the barrier which depends on the potential energy of the elastically deformed lattice is lower and the ionic conductivity is therefore higher.

Approaching the most intense reddish yellow tone of praseodymium doped zircon pigment

Praseodymium doped zirconium silicate pigments (PrxZr1-xSiO4) were synthesized by a solid-state reaction, and the influence of praseodymium fraction (x ​= ​0.03, 0.05 or 0.07), temperature (900, 1000, 1100 or at 1200 ​°C) and calcination time (6, 12, 24 or 48 ​h) was simultaneously tested to determine their effect on colorimetric properties. The chromatic properties are associated with the volume of the unit cell; thus, with the amount of Pr4+ that is integrated into the crystal structure, the ascending concentration of the Pr4+ into zircon structure increases the color intensity only in the range where the unit cell volume is close to 261 ​Å3, lower or higher values result in pigments with lower yellow intensities. An intense reddish-yellow tone can be reached delimited by praseodymium fraction of 0.03 and 0.05, temperature between 900 and 1100 ​°C, and 6 ​h of calcination time.

The influence of nd0 transition metal cations on the Eu3+ asymmetry ratio R=I(5D0−7F2)I(5D0−7F1) and crystal field splitting of 7F1 manifold in pyrochlore and zircon compounds

This paper examines the influence of transition metal cations with empty nd0 cores on the Eu3+ asymmetry ratio R=I(5D0−7F2)I(5D0−7F1) and the magnitude of crystal field splitting of the 7F1 manifold (ΔΕ; 7F1). Two families of compounds that crystallize with the pyrochlore and zircon structures are considered. The pyrochlores under consideration have the general formula La2M2O7 (M = Hf, Zr, Sn). Comparison of the Eu3+ optical properties indicate that R increases in order La2Sn2O7 < La2M2O7 (M = Hf, Zr) while (ΔΕ; 7F1) varies as La2M2O7 (M = Hf, Zr) < La2Sn2O7. The strength of M-O covalent bonding is responsible for these trends. The M-cations in La2M2O7 (M = Hf, Zr) have empty nd0 orbitals that participate strongly in covalent bonding with oxide anions, while the covalent contribution to the Sn4+-O2- bonding is weak due to filled Sn4+ 4d10 core. Mulliken charge calculations of the cations and anions in isostructural pyrochlore compounds are interpreted to indicate the presence of a stronger low-symmetry crystal field component that increases the asymmetry ratio in compounds with cations having empty ndo cores. This stronger covalent bonding is also responsible for decreasing (ΔΕ; 7F1). The second family of compounds under consideration crystallize in the zircon structure with the general formula YZO4 (Z = P, V). Comparison of Mulliken charges of cations and anions in these compounds indicates strong covalent bonding in the vanadate because it contains V5+ transition metal cation with empty 3d0 orbital. It leads to R(YPO4) < R(YVO4) and [YVO4: (ΔΕ; 7F1)] < [YPO4: (ΔΕ; 7F1)]. It is concluded that in isostructural family of compounds, the covalent bonding within the crystal framework determines R and (ΔΕ; 7F1).

Controllable synthesis of pure monodispersed zirconia nanopowders with tetragonal phase

AbstractNanopowders of pure zirconia have been synthesized using citric acid (CA)‐assisted lamellar liquid crystal template method. The microstructure of the zirconia powder prepared at the different mole ratios of CA to zirconium oxynitrate (ZN) was characterized by FT‐IR, X‐ray diffraction (XRD), laser particle size analyzer, Raman spectroscopy, and scanning electron microscope (SEM) methods. The phase structure of the sodium dodecyl sulfate (SDS)/C10H21OH/H2O system before and after adding mixing solution CA and ZN was determined by POM (Polarizing Optical Microscope). The results show that lamellar structure of the SDS/C10H21OH/H2O system after adding mixing solution CA and ZN is stable. The presence of CA inhibits agglomeration and growth of zirconia particle. The crystallite size of zirconia powders decreases and agglomerates lowly with addition of CA. Fourier transform infrared spectrometry (FI‐IR) analyses reveal that the structure of chelating organic complex is maintained in zirconia structure at high‐temperature calcination to cause oxygen vacancies which stabilizes the tetragonal phase of zirconia. The zirconia powders remained the single metastable tetragonal phase at the molar ratios of CA to ZN ranging from 1:3 to 5:1. The crystallite size of zirconia with spherical morphology varied from 32.2 to 20.1 nm with the increase of the molar ratio of CA to ZN in the range of 1:3 to 5:1.

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO4 (M = Ce, U).

Orthosilicates adopt the zircon structure types (I41/amd), consisting of isolated SiO4 tetrahedra joined by A-site metal cations, such as Ce and U. They are of significant interest in the fields of geochemistry, mineralogy, nuclear waste form development, and material science. Stetindite (CeSiO4) and coffinite (USiO4) can be formed under hydrothermal conditions despite both being thermodynamically metastable. Water has been hypothesized to play a significant role in stabilizing and forming these orthosilicate phases, though little experimental evidence exists. To understand the effects of hydration or hydroxylation on these orthosilicates, in situ high-temperature synchrotron and laboratory-based X-ray diffraction was conducted from 25 to ∼850 °C. Stetindite maintains its I41/amd symmetry with increasing temperature but exhibits a discontinuous expansion along the a-axis during heating, presumably due to the removal of water confined in the [001] channels, which shrink against thermal expansion along the a-axis. Additional in situ high-temperature Raman and Fourier transform infrared spectroscopy also confirmed the presence of the confined water. Coffinite was also found to expand nonlinearly up to 600 °C and then thermally decompose into a mixture of UO2 and SiO2. A combination of dehydration and dehydroxylation is proposed for explaining the thermal behavior of coffinite synthesized hydrothermally. Additionally, we investigated high-temperature structures of two coffinite-thorite solid solutions, uranothorite (UxTh1-xSiO4), which displayed complex variations in composition during heating that was attributed to the negative enthalpy of mixing. Lastly, for the first time, the coefficients of thermal expansion of CeSiO4, USiO4, U0.46Th0.54SiO4, and U0.9Th0.1SiO4 were determined to be αV = 14.49 × 10-6, 14.29 × 10-6, 17.21 × 10-6, and 17.23 × 10-6 °C-1, respectively.

Water Formation in Non-Hydrolytic Sol-Gel Routes: Selective Synthesis of Tetragonal and Monoclinic Mesoporous Zirconia as a Case Study.

Several non‐hydrolytic sol–gel syntheses involving different precursors, oxygen donors, and conditions have been screened aiming to selectively produce mesoporous t‐ZrO2 or m‐ZrO2 with significant specific surface areas. The in situ water formation was systematically investigated by Karl Fisher titration of the syneresis liquids. XRD and nitrogen physisorption were employed to characterize the structure and texture of the ZrO2 samples. Significant amounts of water were found in several cases, notably in the reactions of Zr(OnPr)4 with ketones (acetone, 2‐pentanone, acetophenone), and of ZrCl4 with alcohols (benzyl alcohol, ethanol) or acetone. Conversely, the reactions of Zr(OnPr)4 with acetic anhydride or benzyl alcohol at moderate temperature (200 °C) and of ZrCl4 with diisopropyl ether appear strictly non‐hydrolytic. Although reaction time and reaction temperature were also important parameters, the presence of water played a crucial role on the structure of the final zirconia: t‐ZrO2 is favored in strictly non‐hydrolytic routes, while m‐ZrO2 is favored in the presence of significant amounts of water. 1H and 13C NMR analysis of the syneresis liquids allowed us to identify the main reactions responsible for the formation of water and of the oxide network. The morphology of the most interesting ZrO2 samples was further investigated by electron microscopy (SEM, TEM).

Effect of magnesia rich spinel on densification and stabilization behavior of monoclinic zirconia

Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventional sintering technique using commercial monoclinic zirconia, Yttrium oxide and waste-derived magnesia-rich spinel (MMA) powder mixtures. In this study, effect of MMA content and sintering temperature on stabilization and densification properties of zirconia has been duly considered. The obtained results showed that m-ZrO2 in MMA-free Z0 reference specimen is partially stabilized upon temperature rising into tetragonal phase by Y3+ ions diffusion inside zirconia structure. MMA-free Z0 reference specimen sintered at 1600 oC showed m- and t-ZrO2 dual-phase structure with a relative density of 80.2%. Unlike, upon rising the sintering temperature, Z10–Z50 composites containing 10–50 wt% MMA demonstrated higher relative density of more than 99% and showed variant behavior, where their m-ZrO2 is transformed and stabilized into cubic form by diffusion of Y3+, Mg2+ and Al3+ ions inside zirconia lattice structure. The outcomes indicate that MMA has significantly improved both the densification and stabilization behavior of m-ZrO2 through facilitating Y3+ diffusion inside zirconia lattice structure.

Silica-free zirconia from zircon mineral by thermal plasma processing

ABSTRACT Experimental and thermodynamic studies on thermal plasma processing of zircon-carbon mixtures are reported in this paper. Plasma processing of zircon-carbon mixtures to convert the silicate mineral to zirconium dioxide with concurrent removal of silica was studied. Zircon sand was mixed with carbon powder and processed in a specially designed nontransferred arc plasma reactor operated using air as plasma medium. Addition of carbon to zircon facilitated in situ reduction of silica to SiO gas, which escaped with the exhaust gas. More than 96% product purity could be obtained by in-flight removal of silica by processing zircon mixed with sufficient amount of carbon at 25 kW input power. Microstructure analysis showed that in-flight removal of silica facilitated the hexagonal growth pattern and irregularly shaped bulk zirconia crystal structures of monoclinic zirconia. Thermodynamic analysis of in-situ removal of silica by carbo-thermal reduction showed that the amount of carbon had a significant effect. The studies showed that controlled addition of carbon could lower the reaction temperature by more than 500 K and facilitated in situ removal of silica. The studies are technologically relevant and offer useful guidance for making the plasma process economically viable.

Short-range order and electronic structure of radiation-damaged zircon according to X-ray photoelectron spectroscopy

Core-level and valence-band X-ray photoelectron spectroscopy was employed to study the dose-dependent radiation effects in the short-range order and the electronic structure of natural U, Th-bearing zircon near-surface layers. Single crystals from different localities (Ratanakiri, Cambodia; Mud Tank, Australia; Highlands, Sri Lanka) exhibiting wide variations in the accumulated radiation dose D≈(0 ÷ 9.2)·1018 α-decays/g was investigated. The dose values obtained by electron probe microanalysis and Raman micro-spectroscopy were used to correlate the samples with the two percolation transitions (p1, p2) in the amorphous-crystalline structure of damaged zircon. The dose-dependent variations in Eb (530.9–531.3, 101.7–102.4, 182.8- 183.3 eV) and FWHM (1.32–2.57, 1.47–1.77, 1.16 -1.55 eV) of the O1s, Si2p, and Zr3d5/2 core levels, respectively, were attributed to changes in the ensemble of non-equivalent short-range order structures. An increase in the dose resulted in the complication of the oxygen sublattice, with the following nearest environments of O atoms: (1) O (Si, [8]Zr, [8]Zr), Eb = 530.8–531.2 eV, the amount of > ~3.5 apfu (at D p2). For the first time, under an increase in the radiation dose, the oppositely directed changes in the effective charges of Si and Zr cations were detected in damaged zircon. This phenomenon was assigned to an increase in the content of the short-range order fragments characteristic of pure oxides SiO2 (namely, Si-O-Si) and ZrO2 (namely, [7]Zr) as well as to the influence of the anions O (Si, Si, [8]Zr), and the assignment was independently confirmed by the valence band analysis. The sequence of transformations in the Si-O and Zr-O sublattices was shown to be not concurrent: a partial polymerization of SiO4 tetrahedra occurs mainly at low and medium doses (D p2) in the amorphous fraction.

Packing fraction, bond valence and crystal structure of AVO4 (A = Eu, Y) microwave dielectric ceramics with low permittivity

The A3+B5+O4 binary oxides have a variety of different structures—monoclinic, and tetragonal—making them suitable candidates for laser hosts, energy storage, microwave dielectric substrates, etc. In this work, we prepared two tetragonal AVO4 (A = Eu, Y) ceramics with zircon structure. The powder X-ray diffraction (XRD) has been used to study phase purity of the zircon-type AVO4 (A = Eu, Y) ceramics. There was a significant correlation between microwave dielectric properties and relative density. Dense EuVO4 and YVO4 ceramics sintered at 1180 °C and 1240 °C exhibited promising microwave dielectric properties with er = 11.6 and 9.9, Q × f = 46,862 GHz and 56,174 GHz, τf = − 49.6 ppm/°C and − 43.7 ppm/°C, respectively. In addition, the relationship between microwave dielectric properties and crystal structure of AVO4 (A = Eu, Y) ceramics were discussed by packing fraction and bond valence theory in detail.

Morphological and geochemical features of zircon from intrusive rocks of El Sela area, Eastern Desert, Egypt

The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks

Thermodynamics of CeSiO4: Implications for Actinide Orthosilicates

Zircon (ZrSiO4, I41/amd) can accommodate actinides, such as thorium, uranium, and plutonium. The zircon structure has been determined for several of the end-member compositions of other actinides, such as plutonium and neptunium. However, the thermodynamic properties of these actinide zircon structure types are largely unknown due to the difficulties in synthesizing these materials and handling transuranium actinides. Thus, we have completed a thermodynamic study of cerium orthosilicate, stetindite (CeSiO4), a surrogate of PuSiO4. For the first time, the standard enthalpy of formation of CeSiO4 was obtained by high temperature oxide melt solution calorimetry to be -1971.9 ± 3.6 kJ/mol. Stetindite is energetically metastable with respect to CeO2 and SiO2 by 27.5 ± 3.1 kJ/mol. The metastability explains the rarity of the natural occurrence of stetindite and the difficulty of its synthesis. Applying the obtained enthalpy of formation of CeSiO4 from this work, along with those previously reported for USiO4 and ThSiO4, we developed an empirical energetic relation for actinide orthosilicates. The predicted enthalpies of formation of AnSiO4 are then determined with a discussion of future strategies for efficiently immobilizing Pu or minor actinides in the zircon structure.

Isomorphous Substitutions in Luminescent Materials Based on ScVO&lt;sub&gt;4&lt;/sub&gt;

The aim of the paper is to define the limits of substitution and phase stability for solidsolutions of orthovanadates with zircon structure Sc1–xLnxVO4, where Ln is a rare-earth element(REE), Ln = Ce – Lu. The mixing energies (interaction parameters) and critical decompositiontemperatures of Sc1–xLnxVO4 solid solutions with the zircon structure were calculated using thecrystal-energy theory of isomorphous miscibility. Diagram of thermodynamic stability visualizingthe substitution limits (x) by the decomposition temperature or the decomposition temperature bythe substitution limits, the dependencies of the decomposition temperatures on the REE atomicnumbers is presented. This diagram also allows assessing areas of stability, instability, andmetastability for Sc1–xLnxVO4 solid solutions. Results of calculations were compared with literaturedata on thermodynamic stability of solid solutions and on substitution limits. The results of thisstudy can be used in the development of new luminescent materials based on ScVO4 modified withREE, in the selection of REE for matrix and activator, in defining optimal proportions of REE inSc1–xLnxVO4 matrices.

Physical characterization and in vitro evaluation of 3D printed hydroxyapatite, tricalcium phosphate, zirconia, alumina, and SiAlON structures made by lithographic ceramic manufacturing

Physical characterization and in vitro evaluation of 3D printed hydroxyapatite, tricalcium phosphate, zirconia, alumina, and SiAlON structures made by lithographic ceramic manufacturing

Cathodic activation of synthesized highly defective monoclinic hydroxyl‐functionalized ZrO 2 nanoparticles for efficient electrochemical production of hydrogen in alkaline media

The high electrochemical stability of Zirconia (ZrO2) at high potentials strongly suggested it as an alternative to carbon supports, which experience reduced efficiency due to some corrosion problems particularly during prolonged electrocatalysis activity. However, the use of ZrO2 was limited by its low electrical conductivity and surface area. In this work, we developed a methodology for synthesizing monoclinic ZrO2 NPs with increased surface area and improved electrical/electrocatalytic characteristics without using any carbon-based co-support material or any metallic nanoparticles. In this context, for the first time, highly defective hydroxyl-functionalized ZrO2 NPs (designated here as ZT NPs) were prepared by a hydrothermal route in the presence of sodium tartrate as a mineralizer. XRD analysis demonstrated that the produced zirconia was semicrystalline microspheres, consisting of monoclinic ZrO2 NPs with high lattice defects. The addition of tartrate ions decreased the crystallite size and increased the defects and microstrain. At the same time, the alkaline hydrogen evolution reaction (HER) catalytic activity of ZrO2 NPs was significantly increased when using sodium tartrate as mineralizer; the overpotential required to obtain 10 mA cm−2 (η10) dropped down from 490 to merely 235 mV, while an exchange current density (jo) increased 12 times to 0.22 mA cm−2. The presence of structural defects (revealed by XRD) and the increased number of active surface sites contending O-H groups (evidenced from ATR-FTIR and XPS) as well as the enhanced electrochemical active surface area (confirmed from double-layer capacitance measurements) were the main reasons behind the high catalytic performance. The ZrO2 NPs catalytic activity increased even further during the long-term stability tests under severe cathodic conditions (ZT*, ZrO2 NPs obtained after the long-term stability, has jo = 0.47 mA cm−2 and η10 = 140 mV), approaching the activity of Pt/C catalyst. This process was assisted by mineralizer removal from the catalyst (testified by XPS). Our studies revealed that ZT* are characterized by larger electroactive surface area and more structure defects compared to ZT, where surface area and microstrains resulting from surface hydroxylation open cavities in zirconia structure.

Composition and Structure of Zircon from Hydrothermal Uranium Occurrences of the Litsa Ore Area (Kola Region, Russia)

Zircon grains from various metagranitoids (plagio- and monzo-granites, gneisses, metasomatic rocks, and pegmatoid veins) from the Skal’noe and Dikoe sites of the Litsa uranium ore area (Kola Region, Russia) were studied in order to reconstruct the sequence and timing of events in the area and to observe effects of hydrothermal process related to uranium mineralization on structure and composition of zircon. Individual zircon grains were studied by means of laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS), ion microprobe and Raman spectroscopy. Isotopic LA–ICPMS data for the Skal’noye and Dikoe ore occurrences suggest the following age sequence of events in the area: intrusion of plagiogranites—2829 ± 12 Ma, formation of magmatic protolith of gneisses—2781 ± 17 Ma, metamorphism of plagiogranites—2636 ± 34 Ma; intrusion of monzogranites and pegmatoid veins—2549–2526 Ma, hydrothermal event with uranium input—2276 ± 21 Ma, last metamorphism of plagio- and monzo-granites—1892–1696 Ma. Ore-bearing rocks in the area are pegmatoid veins and quartz–feldspar metasomatites which contain uraninite. During a 2.3 Ga hydrothermal process, newly formed zircon rims grew simultaneously with the precipitation of uraninite in the veins and metasomatites. These rims are characterized by high U and rare earth elements (REE) contents (up to 6560 and 8760 ppm, respectively), dark cathodoluminescence, low Th-U ratios (0.1–0.007) and a flat LREE-enriched pattern, in some cases inherited from minerals, dissolved during a hydrothermal event (magmatic plagioclase and probably monazite). Hydrothermal zircon rims grew with partial dissolution of the magmatic zircon, as evidenced by the rounded and curved shapes of zircon cores. The degree of alteration caused by hydrothermal events depends on the uranium content in the pre-existing zircon. The effects of zircon alteration and newly formed zircon composition reflect the redistribution of uranium in rocks.

Fe-doped zirconia nanoparticles with highly negative conduction band potential for enhancing visible light photocatalytic performance

Maintaining a highly negative value of conduction band (CB) potential of photocatalysts through metal doping has been a great challenge. Herein, we investigated the effects of Fe-doping on the crystal structures and electronic structures of zirconia (ZrO2) in detail by combining experiments and Density Functional Theory (DFT). It was revealed that the Fe-doping obviously triggered the formation of tetragonal phase ZrO2 and induced a defect states in the bandgap of Fe-doped ZrO2. Due to the coherent effect between the electrons of the Fe 3d orbitals and ZrO2 intrinsic electronic states, the defect states expanded the light absorption edge of ZrO2 and Fe-doped ZrO2 showed a small bandgap with maintaining a highly negative value of the CB potential. Meanwhile, Fe-doping significantly enhanced photoelectrochemical properties, the efficiency separation of electron-hole pairs and photocatalytic activity in comparison with the pristine ZrO2. We also found that 0.5%Fe-ZrO2 exhibited the optimum photocatalytic performance, and reached 96% for degradation of Rhodamine B (RhB) within 150 min under visible light irradiation. This work elucidated the mechanism of the photocatalytic degradation of RhB over Fe-doped ZrO2 and provided a promising approach in designing highly negative CB potential of ZrO2 via Fe doping toward sustainable environmental remediation.