Liquid Phase Precursor Research Articles

Preparation of (Zr0.25Hf0.25Ta0.25Nb0.25)C high-entropy ceramic nanopowders via liquid-phase precursor route at a low temperature of 1500 °C

Using citric acid, ethylene glycol, ZrOCl2·8H2O, HfOCl2·8H2O, NbCl5, and TaCl5 as raw materials, based on the principle of Pechini coordination polymerization, the (Zr0.25Hf0.25Ta0.25Nb0.25)C high-entropy ceramic precursor solution was successfully prepared, and the corresponding high-entropy ceramic powder was formed by pyrolysis at a low temperature of 1500 °C. The molecular structure of the precursor and its pyrolysis products were analyzed and characterized by different analytical and testing methods. The results show that in the precursor solution, the organic compound and the metal ions form a stable three-dimensional macromolecular structure, so that the metal ions show a uniform distribution at the molecular level, shortening the diffusion path during the carbothermal reduction reaction, thereby enabling the formation of the single-phase high-entropy carbide ceramic powders at a relatively low temperature. The obtained ceramic powders have high purity, uniform element distribution, with an average particle diameter of approximately 42 nm and an oxygen content of about 1.61 wt%. The precursor solution prepared in this study has a moderate viscosity of 20–50 mPa s and a high ceramic yield of 45 %, which is ideal for the preparation of high-entropy ceramic matrix composites.

Synthesis and oxidation behavior of Ti-Zr-Ta(Hf) high entropy carbide nanopowders by sol-gel method

Multi-component solid solution carbide is a promising material due to its excellent mechanical strength, thermal stability, and resistance to chemical corrosion. In this study, we intentionally designed and synthesized three types of solid solution carbide powders using the sol-gel method: (Ti1/3Zr1/3Ta1/3)C, (Ti1/3Zr1/3Hf1/3)C and (Ti1/4Zr1/4Ta1/4Hf1/4)C. The results show that the liquid-phase precursor undergoes pyrolysis at 800 °C and subsequently form homogeneous single face-centered cubic structure solid solutions upon thermal treatment at temperatures exceeding 1800 °C. The obtained powders exhibited ultra-fine and uniform particle sizes of 340 nm, 248 nm, and 401 nm, respectively. Furthermore, the oxidation behavior of the three types of carbide powders in air shows that Hf and Ta elements are of great significance in improving oxidation resistance. The solid solution of Hf increases the initial oxidation temperature, while Ta tends to form a complex oxide with Zr, which helps to improve the oxidation temperature resistance. This work therefore contributes filling the gap of employing the sol-gel method in the fabrication of multi-component solid solution carbide materials and provides novel insights into their synthesis mechanism and oxidation behaviours.

Recycling of fly ash to synthesize zeolites for efficient removal of dioxins

The large amount of fly ash (FA) produced by coal-fired power plants places tremendous pressure on the environment. Meanwhile, toxic dioxins emitted from municipal solid waste incineration plants are of great concern. To address these challenges, a win-win approach was proposed to re-utilize FA for synthesis of zeolite materials for dioxins adsorption. The results indicate that the Si/Al molar ratio in the liquid-phase precursor significantly influences the distribution of Si-Al 4-membered rings (Si/Al=1) and Si-Al 4-membered rings (Si/Al=3) in the system. These units are key secondary structures of the zeolite skeleton, determining the proportions of A-type and X-type zeolites in the product. With the increasing Si/Al molar ratio of precursor, the specific surface area and Si/Al molar ratio of zeolites derived from fly ash (ZFA) both increased, while they played a positive and negative role in dioxins adsorption, respectively. The adsorption of dioxins by ZFA peaked at a Si/Al molar ratio of precursor of 1.5, reaching 4.13×105 pg I-TEF/g, surpassing activated carbon by 1.46 times. This study not only elucidates the mechanism of Si/Al molar ratio of precursor on crystalline transformation of ZFA, but also confirms the potential of ZFA in dioxins adsorption.

Band Gap Engineering of MoxW1-xS2 Alloy Monolayers with Wafer-Scale Uniformity.

Modulating the band gap of two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors is critical for their application in a wider spectral range. Alloying has been demonstrated as an effective method for regulating the band gap of 2D TMDC semiconductors. The fabrication of large-area 2D TMDC alloy films with centimeter-scale uniformity is fundamental to the application of integrated devices. Herein, we report a liquid-phase precursor one-step chemical vapor deposition (CVD) method for fabricating a MoxW1-xS2 alloy monolayer with a large size and an adjustable band gap. Good crystalline quality and high uniformity on a wafer scale enable the continuous adjustment of its band gap in the range of 1.8-2.0 eV. Density functional theory calculations provided a deep understanding of the Raman-active vibration modes of the MoxW1-xS2 alloy monolayer and the change in the conductivity of the alloy with photon energy. The synthesis of large-area MoxW1-xS2 alloy monolayers is a critical step toward the application of 2D layered semiconductors in practical optoelectronic devices.

Phase-Tunable Molybdenum Boride Ceramics as an Emerging Sensitive and Reliable SERS Platform in Harsh Environments.

Traditional surface-enhanced Raman scattering (SERS) sensors rely heavily on the use of plasmonic noble metals, which have limitations due to their high cost and lack of physical and chemical stability. Hence, it is imperative to explore new materials as SERS platforms that can withstand high temperatures and harsh conditions. In this study, the SERS effect of molybdenum boride ceramic powders is presented with an enhancement factor of 5 orders, which is comparable to conventional noble metal substrates. The molybdenum boride powders synthesized through liquid-phase precursor and carbothermal reduction have β-MoB, MoB2, and Mo2B5 phases. Among these phases, β-MoB demonstrates the most significant SERS activity, with a detection limit for rhodamine 6G (R6G) molecules of 10-9m. The impressive SERS enhancement can be attributed to strong molecule interactions and prominent charge interactions between R6G and the various phases of molybdenum boride, as supported by theoretical calculations. Additionally, Raman measurements show that the SERS activity remains intact after exposure to high temperature, strong acids, and alkalis. This research introduces a novel molybdenum boride all-ceramic SERS platform capable of functioning in harsh conditions, thereby showing the promising of boride ultrahigh-temperature ceramics for detection applications in extreme environments.

In-situ synthesis of hierarchically high porosity ZrB2 ceramics from carbon aerogel template with excellent performance in thermal insulation and light absorption

This work introduces an innovative methodology combining the in-situ boron/carbon thermal reduction (BCTR) reaction and replication carbon aerogel template to synthesize hierarchically high porosity ZrB2 ceramics. The meticulously designed ceramic liquid-phase precursor ensures higher solubility of solutes while reducing the temperature requisite for boron/carbon thermal reduction. An additional carbon source is incorporated in the precursor to ensure the uniformity of resulting ZrB2 grains, concurrently maintaining ZrB2 phase purity. The ultimate prepared ZrB2 porous ceramics present a uniform microstructure, with grain sizes at the hundred-nanometer scale, and exhibit a hierarchical pore structure. The ZrB2 porous ceramics exhibited high porosity (85.4–92.9%), low density (0.264–0.482 g/cm3), reasonable compressive strength (0.26–0.51 MPa), low thermal conductivity (0.103–0.212 W/m·K), and efficient light absorption in the range of 400–2000 nm (>94%). The fabricated ZrB2 porous ceramics hold significant promise for applications in high-temperature insulation and light absorption within elevated-temperature environments.

Synthesis and formation mechanism of HfB2 ultrafine powders with low oxygen via flocculating settling assisted process and carbo/borothermal reduction

In this study, ultrafine HfB2 powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors. The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions, and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders. The as-resulted quasi-spherical HfB2 powders under the optimum conditions (atomic molar ratio M:B:C = 1:2.8:10) calcined at 1500 °C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%. Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO2 cores. We reveal that below 1300 °C, HfC is not an intermediate product of HfB2 powder during the transition of precursors. Instead, HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process. The proposed formation mechanism of HfB2 is completely different from the traditional two-step transformation method. After the sintering of the ultrafine powders, the HfB2 ceramics show a relative density of 96.1% and superior mechanical properties compared to other works. Furthermore, by simply replacing the initial metal source, chlorinated group IV and V transitional metals (Ti, Zr, Ta, Nb) can also convert into high-purity and ultrafine diborides. This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.

Microwave-assisted synthesis and luminescence properties of NaYb1-xErxGeO4, NaY1-yYb3y/4Ery/4GeO4 olivines

A new series of olivine-type NaYb1-xErxGeO4 (x ​= ​0.0–0.35), NaY1-yYb3y/4Ery/4GeO4 (y ​= ​0.0–0.6) germanates has been prepared by the liquid-phase precursor method with further microwave annealing for the first time. It has been found that synthesized samples yield upconversion luminescence in the range of 400–900 ​nm under 980 ​nm laser diode excitation The concentration and excitation power dependences of emission intensity have been investigated. The mechanisms of upconversion luminescence as well as concentration quenching have been proposed. In addition, the dependence of the ratio between luminescence peaks at 534 and 560 ​nm on temperature has been studied at 298–498 ​K. The absolute (Sa) and relative (Sr) sensitivities reach maximum values of 0.66% ​× ​K−1 at T = 473 K and 1.05% ​× ​K−1 at T ​= ​298 ​K, respectively. The obtained data indicate the perspectives of using of NaY0.8Yb0.15Er0.05GeO4 sample as an active optical component for non-contact thermometers.

Thickness dependence of resistive switching characteristics of the sol–gel processed Y2O3 RRAM devices

In this study, yttrium oxide (Y2O3)-based resistive random-access memory (RRAM) devices were fabricated using the sol–gel method. The fabricated Y2O3 RRAM devices exhibited conventional bipolar RRAM device characteristics and did not require a forming process. The Y2O3 film thickness was controlled by varying the liquid-phase precursor concentration. As the concentration increased, thicker Y2O3 films were formed. In addition, the concentration of oxygen vacancies increased. The RRAM device properties were not observed for thin Y2O3 films, which had the lowest oxygen vacancy concentration. Moreover, RRAM devices, which consisted of the thickest Y2O3 films with the largest oxygen vacancy concentration, showed poor non-volatile properties. The optimized Y2O3-based RRAM devices with a thickness of 37 nm showed conventional bipolar RRAM device characteristics, which did not require an initial forming process. The fabricated RRAM devices showed a high resistance state to low resistance state ratio of over 104, less than +1.5 V of SET voltage, and −15.0 V of RESET voltage. The RRAM devices also showed promising non-volatile memory properties, without significant degradation after 103 s retention and 102 cycle endurance tests.

Strong green-emission phosphor Ca2SiO4:Eu2+ to achieve the color constancy and high luminous efficiency for white LEDs

The study uses the green phosphor of Ca2SiO4:Eu2+ to achieve the color constancy for the dual-film remote phosphor white-LED model at low as well as big CCTs. The utilized green phosphor Ca2SiO4:Eu2+ was prepared using the water-soluble-silicon liquid phase precursor method with the doped Eu2+ ion concentration of 3 mol%. The Ca2SiO4:Eu2+ phosphor emits strong green light with emission intensity focused at 502 nm wavelength, and a wide stimulation band of colors of 225 nm – 450 nm. After applying the Ca2SiO4:Eu2+ green phosphor and modifying its concentration, the modified color and luminous performances can be observed. The better color uniformity and higher luminescence efficiency can be obtained by increasing the percentage of Ca2SiO4:Eu2+ in the phosphor configuration. Meanwhile, the color rendering metrics tend to reduce slightly when the concentration of Ca2SiO4:Eu2+ is over 10% wt.

Using liquid phase precursor method to create a high-efficiency Ca<sub>2</sub>SiO<sub>4</sub>:Eu<sup>2+</sup> green-emitting phosphor

A standard solid-state reaction (SSR), a new fluid phase preparatory method utilizing LPP-SiO2(sol), and a water-based soluble silicone compound were employed to manufacture green Eu2+-based Ca2SiO4 phosphors liquid phase precursor (LPP-WSS). The generated phosphors feature large excitation spectra in the range of 225–450 nm and a strong green emission reaches the peak value at 502 nm owing to a 4f65d1→4f7(8S7/2) transition of Eu2+. These samples burned at 1100 1C produce the highest luminous intensity. The luminous properties of phosphors, which are manufactured by the liquid phase precursor LPP-WSS technique, were investigated at the range of 0.1-5.0 mol percent of Eu2+, with the maximum emission density observed at the value of 3.0 mol percent of Eu2+. The phosphors produced by the LPP-WSS technique exhibited a more uniform phase dispersion and higher luminous strength than those produced using the other procedures, according to a detailed report based on numerous characterizations. As a result, Ca2SiO4:Eu2+ has an indisputable possibility in white light-emitting diodes WLEDs and fluorescent lighting.

Изучение литийпроводящей керамики Li1.3Al0,3Ti1,7(PO4)3 со структурой NASICON

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 ceramics with a high-density was obtained from powders synthesized from a liquid-phase precursor. The technological scheme of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte production is given. It is established that at 800 °C a single-phase well-crystallized Li1.3Al0.3Ti1.7(PO4)3 is formed. The ionic conductivity of the sintered Li1.3Al0.3Ti1.7(PO4)3 tablets (density 88–90 %) was 1,9·10–4 S/cm at room temperature, and the electronic conductivity did not exceed 5·10–10 S/cm. The Li+ ion transfer number, measured by potentiostatic chronoamperometry, was 0.99, indicating that the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 is a purely ionic conductor.

Anisotropic Magnetism in Gradient Porous Carbon Composite Aerogels

Porosity is of high importance for functional materials, as it allows for high surface areas and the accessibility of materials. While the fundamental interplay between different pore sizes and functionalities is quite well understood, few studies on gradually changing properties in a material exist. To date, only a few examples of such materials have been synthesized successfully. Herein, we present a facile method for synthesizing macroscopic carbon aerogels with locally changing pore sizes and functionalities. We used ultracentrifugation to fractionate differently functionalized and sized polystyrene nanoparticles. The assembly into gradient templates was conducted in a resorcinol–formaldehyde (RF) sol, which acted as a liquid phase and carbon precursor. We show that the modification of nanoparticles and a sol–gel precursor is a powerful tool for introducing dopants (sulfur and phosphorous) and metal nanoparticles (e.g., Ni) into gradient porous carbons formed during the carbonization of the RF sol. Understanding the underlying interactions between particles and precursors will lead to a plethora of possibilities in the material design of complex functionally graded materials. We showed this by exchanging parts of the template with magnetite–polystyrene composites as templating nanoparticles. This led to the incorporation of magnetite nanoparticles in the formed gradient porous carbon aerogels. Finally, gradually increasing concentrations of magnetite were obtained, ultimately leading to macroscopic carbon aerogels with locally changing magnetic properties, while the graded porosity was maintained.

Influence of Bi2O3 co-doping on Cr-doped ZnGa2O4 red persistent phosphors synthesized by a liquid phase precursor process

The long persistence luminescent property of Cr-doped ZnG2O4 phosphor in the deep red/near-infrared region has been of great interest for the purpose of in vivo bioimaging application. Improving the optical property and afterglow lifetime of this material remain challenging. The microcrystalline cellulose assisted liquid phase precursor process was developed for the synthesis of high-quality ZnGa2O4 phosphors, which process enables uniform distribution of the dopant and co-dopant. In this paper, the co-doping of Bi enhanced the photoluminescence intensity by about 2.5 times, while significantly improving the long afterglow property. Investigation of the influence of the Bi addition indicated that the co-doping Bi not only serves to purify Cr ions in ZnGa2O4, but also brings about the growth of particles and changes in morphology through the role of flux.

Stereolithography additive manufacturing and sintering approaches of SiC ceramics

Stereolithography additive manufacturing (SL-AM) has been reported to produce SiC ceramic recently. However, both the density and strength of the stereolithography additive manufactured SiC ceramic need to be improved. In this study, different sintering approaches, including liquid phase sintering (LPS), precursor infiltration and pyrolysis (PIP), and liquid silicon infiltration (LSI), were applied based on the SL-AM prepared SiC green bodies. SiC sintered bodies were finally obtained. In each condition, the relative density, crystalline phases, microstructure, and flexural strength were investigated in detail. The relative density of the LPS-sintered SiC, PIP-sintered SiC, and LSI-sintered SiC ceramics were 78.2 ​± ​1.36%, 82.6 ​± ​0.48%, and 96.2 ​± ​0.32%, respectively. And the strength of the LPS-sintered SiC, PIP-sintered SiC, and LSI-sintered SiC body were 77 ​± ​5.2 ​MPa, 184.2 ​± ​8.5 ​MPa, and 210.4 ​± ​10.3 ​MPa, respectively. The density and strength were compared to each other, as well as other additive manufacturing results and traditional results. At last, LSI is found to be the most promising sintering approach for stereolithography additive manufactured SiC ceramic.

Ultrafast growth of nanocrystalline graphene films by quenching and grain-size-dependent strength and bandgap opening

Nanocrystallization is a well-known strategy to dramatically tune the properties of materials; however, the grain-size effect of graphene at the nanometer scale remains unknown experimentally because of the lack of nanocrystalline samples. Here we report an ultrafast growth of graphene films within a few seconds by quenching a hot metal foil in liquid carbon source. Using Pt foil and ethanol as examples, four kinds of nanocrystalline graphene films with average grain size of ~3.6, 5.8, 8.0, and 10.3 nm are synthesized. It is found that the effect of grain boundary becomes more pronounced at the nanometer scale. In comparison with pristine graphene, the 3.6 nm-grained film retains high strength (101 GPa) and Young’s modulus (576 GPa), whereas the electrical conductivity is declined by over 100 times, showing semiconducting behavior with a bandgap of ~50 meV. This liquid-phase precursor quenching method opens possibilities for ultrafast synthesis of typical graphene materials and other two-dimensional nanocrystalline materials.

Growth of Nb-Doped Monolayer WS2 by Liquid-Phase Precursor Mixing.

Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p-type conductivity in MoS2 and WS2 is challenging because of their natural tendency to form n-type vacancy defects. Here, we report versatile growth of p-type monolayer WS2 by liquid-phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with different concentrations of substitutionally doped Nb up to 1014 cm-2 can be grown by reacting solution-deposited precursor film with sulfur vapor at 850 °C, reflecting the good miscibility of the precursors in the liquid phase. Atomic-resolution characterization with aberration-corrected scanning transmission electron microscopy reveals that the Nb concentration along the outer edge region of the flakes increases consistently with the molar concentration of Nb in the precursor solution. We further demonstrate that ambipolar field-effect transistors can be fabricated based on Nb-doped monolayer WS2.

Synthesis of high-efficiency red-emission Ca14Zn6Al9.97Mn0.03O35 phosphors with particle control

Highly efficient Ca14Zn6Al9.97-Mn0.03O35 (CZAMO) red phosphors with various-sized particles from the nano to the micron size were synthesized using the liquid phase precursor (LPP) method. The particle size of the CZAMO phosphor obtained at 1000 °C is less than 150 nm, but it grew to the micron sizes with the increasing of the firing temperature. The red-emission wavelength range of the CZAMO phosphors is from 650 to 750 nm with the 713-nm emission peak (excited at 450 nm). When the CZAMO phosphor synthesized by LPP method (L-CZAMO) was compared with CZAMO phosphor synthesized by the solid states reaction (SSR) method (S-CZAMO), the photoluminescence (PL) intensity of the L-CZAMO is four times larger (14% higher) than that of the S-CZAMO at 1000 °C (1200 °C).

Synthesis design of Y3Al5O12: Ce3+ phosphor for fabrication of ceramic converter in automotive application

A cellulose-assisted, liquid-phase precursor (LPP) was used to synthesize a YAG phosphor radiating near 530 nm with a particle size of 400 nm, which may be implemented in many applications. The mixture of the materials was homogeneous, and the cellulose-assisted LPP method involved a liquid-phase reaction at a lower temperature compared to a solid-state reaction (SSR). The reaction was performed at 1200, 1300 and 1400 °C, and the composition ratio of the samples was controlled based on yttrium (L1: 2.7, L2: 2.8, L3: 2.9, L4: 2.95, and L5: 3.1 M). ∼400 nm particles were obtained at 1200 °C and ∼1 μm at 1300 °C. At 1200 °C, the PL intensity was the highest in the Y3.1Al5O12 sample. At 1300 and 1400 °C, the strongest intensity was evident in the Y2.9Al5O12 sample. The XRD patterns for all temperatures showed a YAG phase in JCPDS.

Sensitized IR luminescence in Ca3Y2Ge3O12: Nd3+, Ho3+ under 808 nm laser excitation

A promising series of infrared phosphors Ca3Y2-х-yNdxHoyGe3O12 (x = 0.0–0.3; y = 0.000015–0.15) with garnet structure has been prepared using a liquid-phase precursor method. The room temperature X-ray powder diffraction study and density functional theory (DFT) calculations show consistently that incorporated trivalent neodymium ions occupy calcium dodecahedral sites, whereas ousted part of calcium ions moves into yttrium/holmium octahedral sites. DFT calculations and results of diffuse reflectance measurements reveal that an increase in the neodymium concentration and, consequently, the degree of cation substitution leads to a noticeable band gap reduction. The infrared luminescence in range from 1.0 to 3.4µm for Ca3Y2-х-yNdxHoyGe3O12 is observed under 808nm laser diode excitation. The trace amount of holmium ions and a low doping ratio of Ho3+ and Nd3+ ions allow revealing of intense emission at 2.0–3.4µm region. The highest emission intensity is attained at x = 0.15 in Ca3Y2-хNdxGe3O12:Ho3+. The concentration quenching of Ho3+ emission in the Ca3Y1.85–yNd0.15HoyGe3O12 solid solutions is observed at the activator content of y > 1.5·10−4. A very weak red upconversion emissions at 650 and 740nm were observed upon 808nm laser diode excitation. The proposed mechanism for multistage process of energy transfer between the active centers involves the participation of Nd3+ ions as sensitizers of infrared luminescence of Ho3+ ions. The results indicate that the Ca3Y2-х-yNdxHoyGe3O12 germanate can be considered as a promising material for near- and middle infrared phosphors.