Showing papers on "Orthorhombic crystal system published in 2022"
TL;DR: In this article , the structural stability, electronic and optical properties of VH2 hydrides are investigated, and the first-principles method is applied to study the structural and electronic properties.
59 citations
TL;DR: In this article , a series of high quality rare earths (RE) based magnetic materials have been fabricated and a combination of theoretical and experimental investigation has been performed in terms of the crystal structure, electronic structure, magnetic properties and magnetic phase transition (MPT) as well as the magnetocaloric (MC) effect has been extensively investigated in various magnetic materials.
48 citations
TL;DR: In this paper , the ab-initio calculation is used to study the structure and hydrogen evolution catalytic activity of the two novel borophene structures (orthorhombic: Pmmn and hexagonal: Pmmm ), and the triangular-type borophane structure for comparison.
41 citations
TL;DR: In this paper , the incommensurate phase is modulated by stabilizing the antiferroelectric phase and the energy storage performance of the infomagnetic phase under ultrahigh electric field is studied.
Abstract: An incommensurate modulated antiferroelectric phase is a key part of ideal candidate materials for the next generation of dielectric ceramics with excellent energy storage properties. However, there is less research carried out when considering its relatively low polarization response. Here, the incommensurate phase is modulated by stabilizing the antiferroelectric phase and the energy storage performance of the incommensurate phase under ultrahigh electric field is studied. The tape‐casting method is applied to construct dense and thin ceramics. La3+ doping induces a room‐temperature incommensurate antiferroelectric orthorhombic matrix. With little Cd2+, the extremely superior energy storage performances arose as follows: when 0.03, the recoverable energy storage density reaches ≈19.3 J cm‐3, accompanying an ultrahigh energy storage efficiency of ≈91% (870 kV cm‐1); also, a giant discharge energy density of ≈15.4 J cm‐3 emerges during actual operation. In situ observations demonstrate that these superior energy storage properties originate from the phase transition from the incommensurate antiferroelectric orthorhombic phase to the induced rhombohedral relaxor ferroelectric one. The adjustable incommensurate period affects the depolarization response. The revealed phase‐transition mechanism enriches the existing antiferroelectric–ferroelectric transition. Attention to the incommensurate phase can provide a reference for the selection of the next generation of high‐performance antiferroelectric materials.
37 citations
TL;DR: In this paper , the effect of biaxial strain on the electronic and optical properties of orthorhombic two-dimensional AlBrSe monolayer was investigated by the first-principles calculations.
36 citations
TL;DR: In this article , three ternary rare earth (RE) based carbide compounds were synthesized, an investigation of combined experimental and theoretical has been performed with regard to crystal structure, magnetic properties, magnetic phase transition as well as the magnetocaloric effect (MCE) and magnetoric performance.
36 citations
TL;DR: In this article, a new type of microwave dielectric ceramics was fabricated through a traditional solid-phase method, which can be synthesized and densified at 950°C, and the crystal structure of KSrPO4 was further confirmed by Rietveld refinement analysis.
34 citations
TL;DR: In this article , X-ray diffraction assisted Rietveld refinement of representative YAlO3:xSm3+ (x = 0.01 to 0.04 mol) nanocrystalline materials were synthesized successfully through solution combustion (SC) synthetic method.
31 citations
TL;DR: In this article , a new type of microwave dielectric ceramics was fabricated through a traditional solid-phase method, which can be synthesized and densified at 950 °C, and the crystal structure of KSrPO4 was further confirmed by Rietveld refinement analysis.
29 citations
TL;DR: In this paper , the intrinsic ferroelectricity in Y-doped HfO2 epitaxial thin films was shown to increase spontaneous polarization up to a record-high 50 ¼ c/cm2 value at room temperature.
Abstract: Ferroelectric HfO2-based materials hold great potential for widespread integration of ferroelectricity into modern electronics due to their robust ferroelectric properties at the nanoscale and compatibility with the existing Si technology. Earlier work indicated that the nanometer crystal grain size was crucial for stabilization of the ferroelectric phase of hafnia. This constraint caused high density of unavoidable structural defects of the HfO2-based ferroelectrics, obscuring the intrinsic ferroelectricity inherited from the crystal space group of bulk HfO2. Here, we demonstrate the intrinsic ferroelectricity in Y-doped HfO2 films of high crystallinity. Contrary to the common expectation, we show that in the 5% Y-doped HfO2 epitaxial thin films, high crystallinity enhances the spontaneous polarization up to a record-high 50 {\mu}C/cm2 value at room temperature. The high spontaneous polarization persists at reduced temperature, with polarization values consistent with our theoretical predictions, indicating the dominant contribution from the intrinsic ferroelectricity. The crystal structure of these films reveals the Pca21 orthorhombic phase with a small rhombohedral distortion, underlining the role of the anisotropic stress and strain. These results open a pathway to controlling the intrinsic ferroelectricity in the HfO2-based materials and optimizing their performance in applications.
27 citations
TL;DR: In this paper , a single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated and a novel mode of lateral polymorphic regrowth was detected.
Abstract: Polymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga_{2}O_{3} and, potentially, for similar polymorphic families in other materials.
TL;DR: In this article , the synthesis and physicochemical characterization of mixed-halide MHyPbBrxCl3-x perovskites (x = 0.40, 0.58, 0., 1.33, 1.95, 2.25, and 2.2) is presented.
Abstract: Three-dimensional lead halide perovskites are promising materials for optoelectronic applications. The most famous representative comprise methylammonium (MA+) and formamidinium (FA+) cations, but recently, this group was enlarged by methylhydrazinium (MHy+) analogues that crystallize in polar structures at room-temperature. Properties of three-dimensional (3D) perovskites can be tuned by mixing of molecular cations or halide anions. Here, we report synthesis and physicochemical characterization of mixed-halide MHyPbBrxCl3–x (x = 0.40, 0.58, 0.85, 1.33, 1.95, 2.25, and 2.55) and MHyPbBr2.8I0.2 perovskites. X-ray diffraction data show that all materials feature a polar monoclinic P21 symmetry at room temperature. With the temperature increase, all MHyPbBrxCl3–x perovskites undergo a displacive phase transition to another polar orthorhombic Pb21m phase at T2 ≥ 318 K. The bromine rich crystals (x ≥ 1.33) exhibit an additional order–disorder phase transition to the archetypal cubic Pm3̅m phase at T1 ≥ 409 K. In contrast to MHyPbBrxCl3–x perovskites, MHyPbBr2.8I0.2 undergoes a direct P21 to Pm3̅m phase transition. The temperature at which the cubic phase is stabilized, stability range of the Pb21m phase, and distortion of the lead-halide octahedra decrease with the increase of Br– content. The structural changes affect dielectric, conductivity, and optical properties. In particular, the Br-rich samples show switchable dielectric behavior near 410–420 K. Furthermore, the activation energy of Cl– ionic conductivity increases with the increase of Br– content in phases Pb21m and P21, whereas in phase Pm3̅m, the conductivity of Br– ions increases with the increase of Cl– content. The energy band gap narrows and the photoluminescence (PL) bands exhibit red shift when going from Cl to Br and then to I. Interestingly, whereas PL of the Br-rich and Cl-rich samples is dominated by bound exciton and self-trapped exciton bands, respectively, these bands are suppressed for 2.25 ≥ x ≥ 0.85. The PL color is strongly tuned by doping and changes from greenish-blue for the Cl-rich samples to yellowish-green for MHyPbBr2.8I0.2. SHG studies demonstrate that doping of MHyPbCl3 with Br– ions reduces the difference between SHG signal intensities of the monoclinic and orthorhombic phases, to the extent that beyond x = 1.95, the SHG response of these phases becomes essentially the same. The relative SHG efficiencies of Br–Cl mixed materials at room temperature increase with the increase in Br content.
TL;DR: In this article , Cs and dimethylammonium cations were incorporated simultaneously into the A-site of perovskite structure to increase the band gap while maintaining the tolerance factor.
TL;DR: In this article , the structural and phase purity of the focused materials have been investigated via X-ray diffraction (XRD) and Fourier transformation infrared (FT-IR) studies.
TL;DR: In this article , a series of Li3−3xM1+xCl6 (−0.14 < x ≤ 0.5, M = Tb, Dy, Ho, Y, Er, Tm) solid electrolytes with orthorhombic and trigonal structures are reported.
Abstract: Understanding the relationship between structure, ionic conductivity, and synthesis is the key to the development of superionic conductors. Here, a series of Li3‐3xM1+xCl6 (−0.14 < x ≤ 0.5, M = Tb, Dy, Ho, Y, Er, Tm) solid electrolytes with orthorhombic and trigonal structures are reported. The orthorhombic phase of Li–M–Cl shows an approximately one order of magnitude increase in ionic conductivities when compared to their trigonal phase. Using the Li–Ho–Cl components as an example, their structures, phase transition, ionic conductivity, and electrochemical stability are studied. Molecular dynamics simulations reveal the facile diffusion in the z‐direction in the orthorhombic structure, rationalizing the improved ionic conductivities. All‐solid‐state batteries of NMC811/Li2.73Ho1.09Cl6/In demonstrate excellent electrochemical performance at both 25 and −10 °C. As relevant to the vast number of isostructural halide electrolytes, the present structure control strategy guides the design of halide superionic conductors.
TL;DR: In this paper , carbon nanotubes (CNTs)-interwoven KFeSO4F microspheres in diethylene glycol (DEG) were used as the cathode to render high performance PIBs, manifesting an outstanding reversible capacity of 110.9 mAh g−1 at 0.2 C, a high working voltage of 3.73 V, and a long-term capacity retention of 93.9% after 2000 cycles at 3 C.
TL;DR: In this article , a new organic-inorganic hybrid, AZEMnBr, has been synthesized and characterized, and the thermal differential scanning calorimetry, differential thermal analysis, and thermogravimetric analyses indicate one structural phase transition (PT) at 346 and 349 K, on cooling and heating, respectively.
Abstract: A new organic–inorganic hybrid, AZEMnBr, has been synthesized and characterized. The thermal differential scanning calorimetry, differential thermal analysis, and thermogravimetric analyses indicate one structural phase transition (PT) at 346 and 349 K, on cooling and heating, respectively. AZEMnBr crystallizes at 365 K in the orthorhombic, Pnma, structure, which transforms to monoclinic P21/n at 200 K. Due to the X-ray diffraction studies, the anionic MnBr42– moiety is discrete. The azetidinium cations show dynamical disorder in the high-temperature phase. In the proposed structural PT, the mechanism is classified as an order–disorder type. The structural changes affect the dielectric response. In this paper, the multiple switches between low- and high- dielectric states are presented. In addition, it was also observed that the crystal possesses a mutation of fluorescent properties between phase ON and OFF in the PT’s point vicinity. We also demonstrate that EPR spectroscopy effectively detects PTs in structurally diverse Mn(II) complexes. AZEMnBr compounds show DC magnetic data consistent with the S = 5/2 spin system with small zero-field splitting, which was confirmed by EPR measurements and slow magnetic relaxation under the moderate DC magnetic field typical for a single-ion magnet behavior. Given the above, this organic–inorganic hybrid can be considered a rare example of multifunctional materials that exhibit dielectric, optical, and magnetic activity.
TL;DR: In this article , the authors proposed a strategy of modulating polarization rotation of lead-free piezoelectric materials to improve the performance of the resulting piezocatalytic activities.
Abstract: The strategy of modulating polarization rotation of potassium sodium-niobate ((K 0.5 Na 0.5 )NbO 3 , KNN) lead-free piezoelectric materials was reported to boost piezoelectric properties and resultant piezocatalytic activities. The effectiveness of modulating polarization rotation was proved by degrading Rhodamine B (RhB) using three KNN-based samples with different phase structures (i.e., orthorhombic (O) phase, orthorhombic-tetragonal (O-T) coexistence phase, and rhombohedral-orthorhombic-tetragonal (R-O-T) coexistence phase). Poled samples with the R-O-T coexistence phase show a reaction rate constant of 0.091 min −1 owing to the easiest polarization rotation, 2.12 times more than that of poled O-phase featured samples with the most difficult polarization rotation. Enhanced piezocatalytic activities primarily originate from the easier polarization rotation and improved carrier concentration, accompanied by the trace of the mechano-charge generation. Therefore, modulating polarization rotation effectively boosts piezocatalysis of KNN-based materials, promising for harnessing natural energy and disease treatment. • lead-free (K, Na)NbO 3 materials are eco-friendly piezocatalyst. • Proposing a new strategy to enhance there piezocatalysis. • Obtaining a high k value of 0.091 min −1 , much superior to those of other materials. • Unveiling the physical mechanisms of the superior piezocatalytic activities.
TL;DR: In this article , a detailed computational approach has been shown to present a complete analysis of four HfO2 polymorphs, outlining the intrinsic properties of each phase on the basis of atomistic displacements.
Abstract: Background: Hafnium Dioxide (HfO2) represents a hopeful material for gate dielectric thin films in the field of semiconductor integrated circuits. For HfO2, several crystal structures are possible, with different properties which can be difficult to describe in detail from an experimental point of view. In this study, a detailed computational approach has been shown to present a complete analysis of four HfO2 polymorphs, outlining the intrinsic properties of each phase on the basis of atomistic displacements. Methods: Density functional theory (DFT) based methods have been used to accurately describe the chemical physical properties of the polymorphs. Corrective Hubbard (U) semi-empirical terms have been added to exchange correlation energy in order to better reproduce the excited-state properties of HfO2 polymorphs. Results: the monoclinic phase resulted in the lowest cohesive energy, while the orthorhombic showed peculiar properties due to its intrinsic ferroelectric behavior. DFT + U methods showed the different responses of the four polymorphs to an applied field, and the orthorhombic phase was the least likely to undergo point defects as oxygen vacancies. Conclusions: The obtained results give a deeper insight into the differences in excited states phenomena in relation to each specific HfO2 polymorph.
TL;DR: In this article , a novel plastic crystal system, that is, carboranes (C2B10H12), including three positional isomers: ortho-, meta-, and para-carborane, which are characterized by C 2v, C2v, D5d point groups, respectively.
Abstract: The discovery of colossal barocaloric effects in organic plastic crystals has significantly advanced the development of solid‐state refrigerant techniques. Adapting to the real application, a tradeoff of various barocaloric performances has to be achieved. Here, it is reported a novel plastic crystal system, that is, carboranes (C2B10H12), including three positional isomers: ortho‐carborane, meta‐carborane, and para‐carborane, which are characterized by C2v, C2v, D5d point groups, respectively. They all undergo an orthorhombic‐to‐tetragonal phase transition around room temperature. Compared to the previously reported organic plastic crystals, this system exhibits a combination of large pressure‐normalized entropy changes, the high‐pressure sensitivity of the transition temperature, small thermal hysteresis, and so forth. Their barocaloric performances are positional‐isomerism dependent, and the best performances are obtained in para‐carborane with maximum entropy changes of about 106.2 J kg−1 K−1 achieved under pressure changes below 30 MPa. This study not only suggests that carboranes would be a considerably promising working material for barocaloric refrigeration at room temperature but also indicates that delicate tuning of molecular isomerism is an effective strategy to enhance barocaloric performances.
TL;DR: In this article , Li-doped CaFe2O4 nanoparticles were synthesized via a facile inexpensive process at low temperature to enhance the electrical conductivity of Li-ion batteries.
TL;DR: In this article, the structure and the radiation shielding efficiency of various types of superconducting ceramics of REBCO (RE: La, Sm, Gd, Eu, Er, Nd, and Dy).
TL;DR: In this paper , the structure and the radiation shielding efficiency of various types of superconducting ceramics of REBCO (RE: La, Sm, Gd, Eu, Er, Nd, and Dy).
TL;DR: In this article, the Pechini method was used to extract structural, morphological, surface and optical characterizations for the nanosized Ba 1-xBixFe1-xCuxO3 (12-50nm) with x values of 0, 0.01, 0.,05, and 0.1.
Abstract: Nanosized Ba1-xBixFe1-xCuxO3 (12–50 nm) with x values of 0, 0.01, 0.05, and 0.1 system was prepared using the Pechini method. Structural, morphological, surface and optical characterizations were performed for the prepared samples. Cubic phase was the predominant phase for the undoped BaFeO3 and Bi and Cu co-doped BaFeO3 samples. Minor phases of monoclinic Ba2Fe2O5, orthorhombic BaFe2O4 and orthorhombic BaCO3 were identified for all the prepared samples. Ba0.95Bi0.05Fe0.95Cu0.05O3 sample has the lowest band gap (2.43 eV). 98.1% paracetamol removal was achieved with 0.75 g/L of Ba0.95Bi0.05Fe0.95Cu0.05O3 at pH 9 after 120 min. The paracetamol degradation follows the pseudo first-order kinetics. HO• is the main oxidative species responsible for the paracetamol degradation. Gas chromatography–mass spectrometry (GC–MS) analysis was performed at the end of the photocatalytic degradation experiment under optimum operating condition using Ba0.95Bi0.05Fe0.95Cu0.05O3 to explain the reaction mechanism and identify the intermediate by-products which is confirmed by ultraviolet/visible (UV/Vis) spectroscopy study at different reaction times.
TL;DR: In this paper , the preparation of centimeter-scale, crack-free, freestanding Hf 0.5Zr0.5O2 (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations and grain boundaries at both the microscopic and mesoscopic scales is reported.
Abstract: Hafnia‐based compounds have considerable potential for use in nanoelectronics due to their compatibility with complementary metal–oxide–semiconductor devices and robust ferroelectricity at nanoscale sizes. However, the unexpected ferroelectricity in this class of compounds often remains elusive due to the polymorphic nature of hafnia, as well as the lack of suitable methods for the characterization of the mixed/complex phases in hafnia thin films. Herein, the preparation of centimeter‐scale, crack‐free, freestanding Hf0.5Zr0.5O2 (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations, and grain boundaries at both the microscopic and mesoscopic scales is reported. Atomic‐level imaging of the plan‐view crystallographic patterns shows that more than 80% of the grains are the ferroelectric orthorhombic phase, and that the mean equivalent diameter of these grains is about 12.1 nm, with values ranging from 4 to 50 nm. Moreover, the ferroelectric orthorhombic phase is stable in substrate‐free HZO membranes, indicating that strain from the substrate is not responsible for maintaining the polar phase. It is also demonstrated that HZO capacitors prepared on flexible substrates are highly uniform, stable, and robust. These freestanding membranes provide a viable platform for the exploration of HZO polymorphic films with complex structures and pave the way to flexible nanoelectronics.
TL;DR: In this paper , the impact of Ta replacement on the structure and energy-storage properties of tungsten bronze ceramics was investigated, and the relationship between structure and electric properties revealed three main conclusions: (1) as the Ta5+ concentration increased, the crystal structure transformed from an orthorhombic Im2a phase to a tetragonal paraelectric P4bm phase.
Abstract: Tungsten bronze ceramics of composition Sr2Ag0.2Na0.8Nb5-xTaxO15 were synthesized by solid state methods to investigate the impact of Ta replacement on the structure and energy-storage properties (ESP). The study on the relationship between structure and electric properties revealed three main conclusions: (1) as the Ta5+ concentration increased, the crystal structure transformed from an orthorhombic Im2a phase to a tetragonal paraelectric P4bm phase; (2) a high recoverable energy storage density (1.44 J/cm3) and a moderate efficiency (82%) under low-electric fields was obtained in x = 0.3 sample; (3) both dielectric properties (−9.6 to 232.7 °C) and ESP (30–150 °C) exhibit an excellent thermal stability for x = 0.3 sample. In addition, a high current density (863.69 A/cm2) and a large powder density (70.21 MW/cm3) were achieved simultaneously. The current system could be a promising candidate in temperature-stable dielectric capacitors under low-fields and over a broad temperature range.
TL;DR: In this article , thin films of BiSbS3 have been successfully synthesized onto well-cleaned soda-lima glass substrates via the chemical bath deposition procedure.
Abstract: In this research work, thin films of BiSbS3 have been successfully synthesized onto well-cleaned soda-lima glass substrates via the chemical bath deposition procedure. The X-ray diffraction patterns of the chemically deposited BiSbS3 films depicted that the synthesized films exposed polycrystalline nature with orthorhombic structure. The analyses of the linear optical parameters of the chemically deposited BiSbS3 thin films refer to improving the values of the absorption coefficient, α and the linear refractive index, n via the increase in the film thickness. In addition, there is an observed reduction in the energy gap, Eg values from 1.38 to 1.22 eV occurred by raising the film thickness. Furthermore, there is an enhancement in the nonlinear optical constants and the optoelectrical parameters occurred by raising the film thickness where the nonlinear refractive index, n2, the optical free carrier concentration, Nopt and the optical conductivity σopt were enlarged with increasing the film thickness.
TL;DR: In this paper , the structural properties, electronic structures, elastic constants, acoustic behaviors, phonon dispersions, optical properties, and various thermophysical properties of binary ortho and hexa-Mo2C (O-MC and H-MC, respectively) compounds were explored via first-principles calculations using the density functional theory.
Abstract: Binary carbides demonstrate attractive set of physical properties that are suitable for numerous and diverse applications. In the present study, we have explored the structural properties, electronic structures, elastic constants, acoustic behaviors, phonon dispersions, optical properties, and various thermophysical properties of binary orthoand hexa-Mo2C (O-MC and H-MC, respectively) compounds in details via first-principles calculations using the density functional theory (DFT). The calculated ground state lattice parameters in both the symmetries are in excellent agreement with available experimental results. The calculated electronic band structure, density of states, and optical properties of Mo2C in both structures reveal metallic features. The orthorhombic crystal shows higher level mechanical and thermal anisotropy compared to that in the hexagonal phase. The elastic constants and phonon dispersion calculations show that, in both structures, Mo2C is mechanically and dynamically stable. A comprehensive mechanical and thermophysical study shows that both phases possess high structural stability, reasonably good machinability, ductile nature, high hardness, low compressibility, high Debye temperature and high melting temperature. Moreover, the electronic energy density of states, electron density distribution, elastic properties, and Mulliken bond population analyses indicate that the structures under consideration consist of mixed bonding characteristics with ionic and covalent contributions. Investigation of the optical properties reveals that the reflectivity spectra are anisotropic with respect to the polarization directions of the electric field in the visible to mid‐ultraviolet regions. High reflectivity over wide spectral range makes the compound suitable as reflecting coating. Both the structures are efficient absorber of ultraviolet radiation. The refractive indices are quite high in the infrared to visible range. Both structures show directional (plane) optical anisotropy. Though, hexa-Mo2C exhibits stronger optical anisotropy than the ortho-Mo2C.
TL;DR: In this article, a single crystal OIH perovskite with 1,5 pentylenediammonium, [NH3-(CH2)5−NH3] MnCl3.47Br0.28 and CoCl2.72Br1.28 was grown from solution by evaporation.
TL;DR: In this paper , two new high-entropy ceramics (HECs) in the weberite and fergusonite structures, along with the unexpected formation of ordered pyrochlore phases with ultra-highentropy compositions and an abrupt pyrotechlore-weberite transition, are discovered in a 21-component oxide system.
Abstract: Abstract Two new high-entropy ceramics (HECs) in the weberite and fergusonite structures, along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition, are discovered in a 21-component oxide system. While the Gibbs phase rule allows 21 equilibrium phases, 9 out of the 13 compositions examined possess single HEC phases (with ultrahigh ideal configurational entropies: ∼2.7 k B per cation or higher on one sublattice in most cases). Notably, (15RE 1/15 )(Nb 1/2 Ta 1/2 )O 4 possess a single monoclinic fergusonite (C2/ c ) phase, and (15RE 1/15 ) 3 (Nb 1/2 Ta 1/2 ) 1 O 7 form a single orthorhombic (C222 1 ) weberite phase, where 15RE 1/15 represents Sc 1/15 Y 1/15 La 1/15 Pr 1/15 Nd 1/15 Sm 1/15 Eu 1/15 Gd 1/15 Tb 1/15 Dy 1/15 Ho 1/15 Er 1/15 Tm 1/15 Yb 1/15 Lu 1/15 . Moreover, a series of eight (15RE 1/15 ) 2+ x (Ti 1/4 Zr 1/4 Ce 1/4 H 1/4 ) 2−2 x (Nb 1/2 Ta 1/2 ) x O 7 specimens all exhibit single phases, where a pyrochlore-weberite transition occurs within 0.75 < x < 0.8125. This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably, as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides. These discoveries expand the diversity and complexity of HECs, towards many-component compositionally complex ceramics (CCCs) and ultrahigh-entropy ceramics.