Conventional Sintering Method Research Articles

Effect of different rare-earth dopings of KNN-based transparent energy storage ceramics

Rare-earth elements [Formula: see text]-, [Formula: see text]-, [Formula: see text]- and [Formula: see text]-doped ([Formula: see text][Formula: see text])[Formula: see text][Formula: see text][Formula: see text][Formula: see text]O3 ceramics (abbreviated as KNLNB-0.1%RE) were prepared by conventional solid-phase sintering method. The structure, transparency, energy storage and photoluminescence properties of the samples are investigated. All ceramics have the pseudo-cubic phase structure without the impurity phase at room temperature. KNLNB-0.1%RE ceramics exhibit excellent optical transmittance, with KNLNB-0.1%Ho achieving 71.8% transmittance in the visible wavelength range (780[Formula: see text]nm) and largest effective energy storage density of 1.45[Formula: see text]J/cm3. In our experiments, rare-earth-doped KNLNB ceramics exhibit photoluminescence effects. This work facilitates the development of transparent energy storage ceramics with fluorescent effects.

Superior dielectric energy storage performance of ultrafine-grained BNT-SBT solid-solution ceramics by solution combustion synthesis

The micrometer scale grain size and large remnant polarization of Bi0.5Na0.5TiO3 (BNT) ferroelectric ceramics severely constrain the breakdown strength and energy efficiency, respectively, restricting their energy storage application despite their large polarization. Hereby, superior energy storage performance is reported by a synergistic strategy of introducing Sr0.7Bi0.2TiO3 (SBT) relaxor ferroelectrics and a solution combustion synthesis (SCS) method. The BNT-SBT solid-solution ceramics are comparatively investigated by the two methods, conventional sintering (CS) and SCS. An ultrafine average grain size of ∼ 0.39 μm was obtained in the SCS-derived ceramic, and thus exhibits an ultra-high critical electric field of 548 kV/cm, and a high recoverable energy density of ∼ 5.69 J/cm3. Those key energy storage parameters are superior to those of the previous reported samples prepared by the CS method. Meanwhile, a high energy efficiency ∼90%, a large power density of ∼ 130.44 MW/cm3 (at 320 kV/cm), and an ultrafast discharge time of ∼ 61.7 ns are also achieved. This study indicates that grain engineering combing with chemical design is an effective way to enhance the dielectric energy storage performance.

Crystal structures, dielectric properties, and lattice vibrational characteristics of Zn1-xCaxWO4 (x = 0-0.25) composite ceramics

In this work, Zn1-xCaxWO4 (x=0-0.25, ZCWO) composite ceramics were prepared by using the conventional solid-state sintering method at 1070 ℃. The impact of Ca2+ substitution on the lattice vibrational characteristics and dielectric responses of the ZCWO composite ceramics was investigated in detail. The formation of composite ceramics was verified by the Rietveld refined X-ray diffraction data of the ZCWO samples. The lattice vibrational characteristics were also identified and analyzed by the Raman and infrared reflection spectra combined with the theoretical simulations. The vibrational modes analysis of the Raman spectra showed that the internal modes of the ZCWO ceramics correspond to the vibrations of the W-O octahedrons. From the Fourier transform infrared reflectance spectra, the existence of three new vibrational modes of Au (315cm-1), Au (834cm-1), and Eu (885cm-1) at x = 0.15-0.25 was observed, which belong to the modes of the CaWO4 ceramic. In addition, the intrinsic dielectric properties fitted by the four-parameter semiquantum model were in direct agreement with the theoretical values obtained from the Clausius-Mossotti & damping equations and the measured values. Besides, the contribution of each lattice vibrational mode to the intrinsic properties of the ZCWO ceramics was thoroughly studied, which shows that external mode 1 contributes the most to the intrinsic properties. The structure-property relationships of the ZCWO ceramics were established using the Raman modes as a media. The optimum dielectric properties of the ZCWO ceramics were obtained when x = 0.25: εr =13.98 (10.48GHz), Q × f = 32,188GHz.

Microstructural characterization and equibiaxial flexural strength of CeO2 and Ti-doped CeO2

In this study, the synthesis of CeO2 and titanium dioxide (TiO2) doped CeO2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO2 dopant concentration was optimized at 0.1 wt % TiO2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. The TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO2, indicating sample chemistry and microstructure impact mechanical behavior for these samples.

Effect of Sm2O3 additive on the microstructure, magnetic and electrical properties of LiTiZn ferrite ceramics

LiTiZn ferrites were prepared by a conventional two-steps solid sintering method. According to X-ray diffraction (XRD) results, the primary phase of all specimens was ferrite spinel. It is shown that Sm2O3 additive 1 wt% slightly reduces the lattice parameter of the spinel phase and leads to the appearance of an additional phase SmFeO3. For the first time for LiTiZn ferrite received, that Sm2O3 additive leads to significant increase of the electrical resistivity and the Curie temperature by 25°. Thus, the problem with dielectric loss reduction in the microwave and thermal stability increasing of ferrite ceramics was solved. At the same time, there is a 6 % decrease in saturation magnetization and 11 % in density while coercive force increases by the 60 %. In addition, scanning electron microscope (SEM) data show significant influence of Sm2O3 additive on grain morphology. The energy dispersive spectroscopy (EDS) patterns confirm SmFeO3 phase formation. The results of the study can be used for improvement of sintering ferrite products in a factory.

Microstructure, dielectric, ferroelectric and piezoelectric properties of K0.45Na0.45Li0.1NbO3 lead-free ceramics prepared via cold sintering with post-annealing

Via the method of cold sintering with post-annealing, the lead-free ceramics [Formula: see text][Formula: see text][Formula: see text]NbO3 were prepared. The cold sintered pellet without post-annealing shows a relative density ([Formula: see text] of 77.9%, which is larger than [Formula: see text] of the green pellet via the conventional solid-state sintering (SSS) method ([Formula: see text]). The cold sintered pellets were post-annealed at temperatures between [Formula: see text]C and [Formula: see text]C. The effect of post-annealing temperatures on microstructure, dielectric, ferroelectric and piezoelectric properties of the ceramics was studied in detail. After being post-annealed, the relative densities and grain sizes of the ceramics were increased. The ceramics post-annealed at [Formula: see text]C show excellent dielectric, ferroelectric and piezoelectric properties. Compared to the conventional SSS method, the method of cold sintering with post-annealing is successful in preparing dense [Formula: see text][Formula: see text][Formula: see text]NbO3 lead-free ceramics in a wide temperature range and at relatively low temperatures.

Flash sintering of ZrO2–SnO2–ZrSnO4 composite nanofibers: Fabrication, properties, and biochemical effects in Drosophila melanogaster

ZrO2–SnO2–ZrSnO4 composite nanofibers (CNFs) were fabricated by an electrospinning technique in three different ratios by volume (%v/v). Changing the composition ratio of CNFs affected the temperature and sinter time variation of both the band gap and the flash sintering (FS) phenomenon. FS experiments were used at a current cut-off of 3.77 mA/mm2 under thermal (844–878 °C) and electric field (420 V/mm). Highly dense CNFs were obtained in less than 80 s with a maximum power absorption of 1.58 W/mm3. In addition to the FS process, CNFs were sintered with the conventional sintering (CS) method at 1200 °C for 1 h. As the amount of Sn in the composition (%v/v) increases, the density increases, but the hardness value decreases. The FS process was proven to produce faster, denser, and harder material than CS.Long-term and permanent results are obtained by designing biocompatible nanocomposite materials in health. However, determining the long-term effects of CNFs, which are considered non-toxic, is necessary. Drosophila melanogaster female food was covered with these different v/v% ratios CNFs (ZrSn, Zr2Sn; 2ZrSn) and contact by life span: The effects were evaluated on movement, weight, egg production, longevity, and antioxidant system (Superoxide dismutase-SOD, catalase-CAT, glutathione-GSH, and 2,2-diphenyl-1-picrylhydrazil-DPPH). It can be said that Zr2S CNFs were not toxic by not changing the life span, egg production, climbing, and biochemical parameters of the fly. However, it was determined that CNFs used in ZrSn and 2ZrSn ratios slightly reduced the behavioral (movement and longevity) and antioxidant activities (SOD and CAT) of the individual.

(Sb0.5Li0.5)TiO3-Doping Effect and Sintering Condition Tailoring in BaTiO3-Based Ceramics.

(1-x)(Ba0.75Sr0.1Bi0.1)(Ti0.9Zr0.1)O3-x(Sb0.5Li0.5)TiO3 (abbreviated as BSBiTZ-xSLT, x = 0.025, 0.05, 0.075, 0.1) ceramics were prepared via a conventional solid-state sintering method under different sintering temperatures. All BSBiTZ-xSLT ceramics have predominantly perovskite phase structures with the coexistence of tetragonal, rhombohedral and orthogonal phases, and present mainly spherical-like shaped grains relating to a liquid-phase sintering mechanism due to adding SLT and Bi2O3. By adjusting the sintering temperature, all compositions obtain the highest relative density and present densified micro-morphology, and doping SLT tends to promote the growth of grain size and the grain size distribution becomes nonuniform gradually. Due to the addition of heterovalent ions and SLT, typical relaxor ferroelectric characteristic is realized, dielectric performance stability is broadened to ~120 °C with variation less than 10%, and very long and slim hysteresis loops are obtained, which is especially beneficial for energy storage application. All samples show extremely fast discharge performance where the discharge time t0.9 (time for 90% discharge energy density) is less than 160 ns and the largest discharge current occurs at around 30 ns. The 1155 °C sintered BSBiTZ-0.025SLT ceramics exhibit rather large energy storage density, very high energy storage efficiency and excellent pulse charge-discharge performance, providing the possibility to develop novel BT-based dielectric ceramics for pulse energy storage applications.

Effect of alumina morphology on flash sintering and mechanical properties of 3YSZ/alumina composites: Whiskers vs powders

In this paper, 3YSZ/alumina composites containing different content of alumina with different forms (powders and whiskers, respectively) were fabricated by flash sintering. The flash sintering behavior and mechanical properties of the composites were characterized and were compared with those prepared by conventional sintering. The onset temperature of the 3YSZ/alumina whiskers composites was lower than that of the 3YSZ/alumina powders composites with identical alumina content. The reason can be attributed to electrical conductivity; the conductivity of the former was lower than that of the latter. For the 3YSZ/alumina powders composites which can be densified by conventional sintering method, their relative density, Vickers hardness and fracture toughness were comparable to those prepared by flash sintering. While for the 3YSZ/alumina whiskers composites where constrained sintering existed, the flash sintering method revealed obvious advantage over the conventional sintering. A relative density of 94.5 %, hardness of 13.77 GPa and fracture toughness of 5.36 MPa m1/2 were obtained for the flash sintered 3YSZ/30 vol% alumina whisker composites. In contrast, the relative density, hardness, and fracture toughness of the conventional sintered ones were 86.4 %, 11.60 GPa and 4.82 MPa m1/2, respectively.

How does cold sintering affect the microstructural evolution of high-entropy pyrochlore during pressureless sintering?

The challenge of producing dense fine-grained high-entropy ceramics is hereby addressed by a combined cold and conventional pressureless sintering method for the first time. It provides nearly fully dense high-entropy pyrochlores with better microstructural homogeneity, and only half the grain size of conventional pressurelessly sintered samples with identical density. Both the finer and more homogeneous microstructures benefit better mechanical properties in hardness and reduced Young’s modulus. The kinetics and activation energies of both densification and grain growth were quantified and discussed to understand how cold sintering affects the microstructural evolution during the following pressureless sintering. More importantly, cathodoluminescence analysis suggested that cold sintering could cause more defects on the surface of the original particles, which could promote the grain boundary diffusion and have drag effects on grain boundary motion. The lessons learned here offer scientific understanding and technological guidance towards pressureless sintering of dense bulk high-entropy ceramics.

Two-stage repeat sintering: A modified method for fabricating hydroxyapatite scaffolds with enhanced mechano-therapeutic properties

A modified two-stage repeat sintering (TSRS) technique has been used to produce hydroxyapatite (HAp) from non-separated animal bones, and the energy consumption per cycle of the proposed TSRS was calculated. The TSRS technique was compared to the conventional one-step sintering method. The energy consumption per cycle of the proposed TSRS was calculated considering economies of scale and typical energy consumption billing in Nigeria. The synthesized powders from both techniques underwent comprehensive characterization through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM). The XRD analysis revealed the main reflections of HAp in the (112), (300), and (202) planes. The FT-IR spectra exhibited characteristic bands representative of HAp at all measurement points. Notably, the TSRS-derived sample during the second sintering step showed carbonate bands, suggesting relevance in the bone structure makeup. SEM images unveiled varying crystal morphologies, ranging from irregular shapes in the raw bone (RB) sample to rounded shapes with nucleation in aggregates and agglomerates at micro and macro levels in the TSRS-derived samples. The samples obtained from the TSRS technique demonstrated a high Ca/P ratio that is potentially beneficial for osteoblast adhesion in vivo. The cost analysis of electricity consumption per TSRS cycle, factoring in economies of scale and typical energy consumption billing in Nigeria, amounted to approximately $8 with consideration of the exchange rates at the time of the study. The microhardness measured using the TSRS technique was 0.5 GPa with a 1 MPa compaction pressure, while the samples prepared using the conventional sintering method were too fragile to handle and measure. The obtained microhardness using the modified technique surpassed values reported in various studies. In conclusion, the samples produced using the TSRS technique exhibited promising results regarding energy efficiency, material characteristics, and microhardness compared to the samples produced through conventional sintering. The distinct crystal morphologies observed suggest potential advantages for biomedical applications, particularly in enhancing osteoblast adhesion.

Effect of sintering mechanism on dielectric properties of Ba0.5Sr0.5TiO3-ZnAl2O4 composite ceramics synthesized by two-step sintering with low energy consumption

The application of Ba1-xSrxTiO3-based composites in microwave field has become a popular research topic. Ba0.5Sr0.5TiO3-ZnAl2O4 (BST-ZA) composite ceramics were successfully fabricated by both conventional sintering and two-step sintering process. The microstructure and dielectric properties of Ba0.5Sr0.5TiO3-ZnAl2O4 composite ceramics prepared by two sintering methods were compared. The samples prepared by the two-step sintering method have lower ion diffusion degree, shorter holding time and lower energy consumption, and it is easier to obtain samples with higher density and uniform grain size distribution, compared with those fabricated by the conventional sintering method. The dielectric permittivity and Curie temperature of two-step sintered samples are lower than those obtained by conventional sintering, while the dielectric tunability is almost unchanged (two-step sintering: 17.7 %, conventional sintering: 18.6 %). These results indicate that two-step sintering method is an efficient and energy-saving method in preparing BST-ZA composites.

Microstructure and mechanical properties of high relative density Ti-48Al-1Fe alloy using irregular blend powder

Conventional pressing and sintering methods provide difficulties in achieving high density for PM TiAl alloys. The Ti-48Al-1Fe alloy was prepared via vacuum pressure-less sintering, and the microstructure evolution and mechanical properties during the sintering densification process of the mixed powder system were investigated. The results shows that the density of the mixed powder reached 98.3 ± 0.14% after pressure-less sintering for 3 hours under high vacuum conditions at 1300°C. The microstructure of the as-sintered alloy is a fine duplex structure composed of α2/γ lamellar colonies and the composite structure. The ultimate tensile strength (UTS) of the as-sintered alloy at room temperature is 315 MPa. The density of the as-sintered alloy reach more than 99.9% after non-capsule hot isostatic pressing (HIP). The as-HIPed alloy exhibits an UTS of 332 MPa at room temperature. At high temperatures, it maintains high strength, with an UTS of 408 MPa and yield strength of 386 MPa at 900°C, which is comparable to that of forged TiAl alloy. Furthermore, the elongation of the sample at 900°C is 20.0%. This process offers a novel method for sintering PM TiAl with high density and mechanical properties at a low cost and near-net shape.

Investigation of the Effect of High-Frequency Induction Sintering on Phase Structure and Microstructure of SiC Reinforced Aluminum Matrix Composites

In this study, SiC-reinforced aluminum matrix composites were powder metallurgically (PM) prepared and sintered using high-frequency induction system (HFIS). The samples with different ratios of SiC (wt.%10, 20 and 40) added to the aluminum matrix were sintered at 660, 800, and 1000 °C. In addition, Al/SiC composites were compared by sintering with the conventional sintering (CS) method under similar sintering conditions. The heating rate for the sintering process using HFIS was 500 °C/min, while the CS method used a heating rate of 10 °C/min. The effect of the temperature and SiC ratio on the density, hardness, phase structure, and microstructure of composites was investigated. The optimum sintering temperature was determined according to the SiC additive amount. When 10%, 20%, and 40% SiC by weight were added to the aluminum matrix in the sintering process with HFIS, the required sintering temperatures were determined as 660, 800, and 1000 °C, respectively. While new phases were not formed as a result of short-term HFIS sintering, a high-temperature Al4C3 phase was detected in CS sintering. HFIS sintered Al/SiC composite samples were obtained in Al and SiC phases with high density and hardness ranging from 43-118 HV. In the high-temperature sintering process with HFIS, the formation of Al4C3 was prevented and its physical and mechanical properties were improved.

Densification of hydroxyapatite through cold sintering process: Role of liquid phase chemistry and physical characteristic of HA powder

Hydroxyapatite is a well-known bioactive material widely employed in bone regeneration applications. Densifying hydroxyapatite at the nanoscale remains challenging with conventional sintering methods. This investigation focuses on the densification of commercially available nano-hydroxyapatite powders through the cold sintering process, utilizing water, acetic acid, and phosphoric acid solutions as transient liquids under 360 MPa pressure at 200 °C. The study systematically examines the influence of physical parameters of hydroxyapatite powder, liquid nature, and ionic concentrations of acid solutions on densification and microstructural characteristics. The relative density of consolidated samples varied with respect to the ionic concentration of the acid solution. Notably, a maximum relative density of 90% has been achieved for hydroxyapatite cold sintered using 2 M phosphoric acid solution without changing the original phase of hydroxyapatite. Overall, this study offers valuable insights into the impact of liquid chemistry on the densification of hydroxyapatite using the cold sintering technique.

Simultaneous laser sintering and embedding of silver nanoparticles for highly flexible embedded electrodes

In manufacturing electronic devices embedded in flexible substrates, persistent technical challenges include process complexity, substrate damage, high surface roughness, and low mechanical flexibility. To address these challenges, this study proposes a method that involves simultaneously sintering silver nanoparticles (Ag NPs) and embedding them in polyethylene terephthalate (PET) substrates to fabricate flexible embedded electrodes. The proposed technique uses laser-generated high-intensity shock waves to compress Ag NPs coated on a PET substrate heated to its glass-transition temperature. The mechanical impact of the shock wave embeds the Ag NPs into the substrate while simultaneously sintering the particles. The thin-film Ag electrode fabricated using the proposed method exhibited outstanding electrical and mechanical properties. The electrical resistivity measured as low as 7.8 μΩ·cm, with a minimal increase of approximately 5 % after 2000 bending cycles at a bending radius of 1 mm. Furthermore, the fracture strength of the fully embedded electrode, as assessed through adhesive tape-peel tests, significantly surpassed that produced through conventional sintering methods. The proposed method has the potential to revolutionize conventional sintering methods in flexible substrate applications, offering a more efficient and reliable method for fabricating flexible embedded electrodes.

Design of TiC intergranular-dispersed Al2O3 composites via in situ and two-step sintering with enhanced mechanical and electrical properties

To further enhance the mechanical properties of the Al2O3/TiC composites and reduce the percolation threshold induced by the controlling microstructures, composites containing 0–20 % TiC were fabricated in this work using the two-step sintering (TSS) method, in which TiC was in situ synthesized from carbon nanotubes and TiH2. From the acquired results, it was indicated that the TiC particles were completely dispersed at the grain boundaries. As the first-step temperature (T1) increased, the Al2O3 grains grew up, while the second-step temperature (T2) mainly affected the densification of the whole structure. The composites could be listed as follows, 1550/1400 > 1600/1400 > 1600/1300 > 1550/1300, which corresponds to a descending order of the balanced Young’s modulus, Vickers hardness, flexural strength, fracture toughness, and electrical conductivity. Moreover, the largest fracture toughness exhibited by 1600/1400-20 was 5.83 MPa m1/2, which increased by 69 % compared with monolithic Al2O3. The similarity of the Al2O3 grain size and the TiC particles size, as well as the complete grain-boundary dispersion of the relatively large TiC particles significantly contributed to the lower percolation value (10.5 %) of the Al2O3/TiC composites produced via the two-step sintering process compared with the composites fabricated by utilizing the conventional single-step sintering (percolation value: 11.2 %) method. The lower percolation value facilitates the fabrication of conductive Al2O3/TiC composites with excellent mechanical properties.

Direct cold sintering of translucent gamma-Al2O3 ceramics

Gamma-Al2O3 ceramics can hardly be densified by conventional sintering methods because of the low surface energy of gamma-Al2O3 powder and phase transformation at elevated temperature. Here, we report the preparation of translucent gamma-Al2O3 ceramics by cold sintering process at merely 350 °C via using the gamma-Al2O3 as starting powder. Due to the enhanced solubility and reaction of gamma-Al2O3 in alkaline solution, the nanocrystalline particles can be densified to ∼92% of full density via adding 10 M NaOH solution as the transient liquid. It is proved that the high concentration of alkaline solution can greatly accelerate the dissolution-precipitation process, leading to the activation energy as low as 16.9 kJ/mol. Consequently, a translucent ceramic with in-line transmittance reaching 16% around 800 nm can be obtained, despite the residual porosity. Considering the stable hardness and translucency after water leaching or heating to 1000 °C, the cold sintered gamma-Al2O3 ceramic may have the potential application as optical windows under extreme environments.

In situ study on enhanced plastic deformability of Lanthanum-doped Bismuth ferrite processed by flash sintering

BiFeO3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 °C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties.

One-step synthesis of single-phase, bulk Bi2Ti2O7 pyrochlores by deep undercooling rapid solidification and its formation mechanism

Preparation of dense Bi2Ti2O7 ceramics with single-phase pyrochlore structure is challenging using the conventional sintering method due to its thermal instability at ≥ 650 °C. Here we synthesized dense and phase-pure Bi2Ti2O7 ceramics from a mixture of Bi2O3 and TiO2 by a novel deep undercooling rapid solidification method using the aerodynamic levitation technique. We reported a surprising discovery that the pyrochlore phase can exist with Bi/Ti ratio varying between 0.9 and 1.1. By a comprehensive investigation on the phase purity, crystal structure, oxidation states and electrical properties, we revealed that the pyrochlore structure is primarily stabilized by the solidification process rather than presence of a large amount of Ti3+. With the advantages of being containerless, one-step and fast processing, deep undercooling rapid solidification is an effective and efficient approach to prepare dense Bi2Ti2O7 pyrochlores, and can be expanded to other thermally unstable compounds to obtain bulk materials.