Single-phase Ceramics Research Articles

The impact of the physicochemical properties of calcium phosphate ceramics on biocompatibility and osteogenic differentiation of mesenchymal stem cells

ObjectiveIn this study we have focused on biocompatibility and osteoinductive capacity analysis of self-manufactured single-phase (HAP) and two-phase (HAP and β-ТСР) bioactive ceramics with various chemical modifications (Fig. 1).ResultsWe demonstrate a reduction in solubility for all analyzed composite after the treatment with H2O and H2O2, accompanied by an enhancement in adsorption activity. This modification also resulted in an increase in micro- and macroporosity, along with a rise in the open porosity. Adipose-derived mesenchymal stromal cells demonstrated excellent cell adhesion and survival when cultured with these ceramics. Calcium phosphate ceramics (H-500, HT-500, and HT-1 series) stimulated alkaline phosphatase expression, promoted calcium deposition, and enhanced osteopontin expression in ADSCs, independently inducing osteogenesis without additional osteogenic stimuli. These findings underscore the promising potential of HAP-based bioceramics for bone regeneration/reconstruction.Graphical

A Novel Microwave Dielectric Ceramic LiSrVO4 for LTCC

Abstract LiSrVO4 (LSV) ceramics were prepared using the solid-state synthesis method, and their phase structure, morphology, sintering characteristics, and microwave dielectric properties were investigated. The LSV ceramics could be densified by sintering at 875–925 °C for 4 hours. XRD indicated that LSV ceramics sintered at 875–925 °C for 4 hours were singlephase ceramics with a monoclinic structure. With the increase in sintering temperature, the dielectric constant and quality factor of LSV ceramics first increased and then decreased, while the temperature coefficient of the resonant frequency gradually decreased. LSV ceramics sintered at 900 °C for 4 hours exhibited a εr of 10.92, a Q×f value of 21115 GHz, and a τf of -4 ppm/°C. LSV ceramics demonstrated good chemical compatibility with silver, showing promising potential in the field of Low-Temperature Co-fired Ceramics.

Investigations of crystal structure, phase compositions and intrinsic dielectric properties of novel Ba2RE2Si4O13 ceramics by bond theory and infrared spectroscopy

Novel Ba2RE2Si4O13 (RE = La, Nd, Sm, Eu, Gd, Ho, Er and Yb) ceramics were prepared by traditional solid reaction methods. The phase compositions of Ba2RE2Si4O13 ceramics were explored. The triclinic structure with P1¯ space group of Ba2RE2Si4O13 ceramics was confirmed by TEM and Rietveld refinement analyses, and the decrease in the ionic radius of RE3+ induced the phase transition from low symmetry (triclinic) to high symmetry (monoclinic) between Ba2Sm2Si4O13 and Ba2Eu2Si4O13. εr-exp of the Ba2RE2Si4O13 ceramics was significantly affected by ionic polarisability. The ‘rattling and compressing effects’ of cations also affected the εr-exp of Ba2RE2Si4O13 ceramics. The intrinsic dielectric loss of Ba2RE2Si4O13 ceramics were evaluated by the far-IR reflectivity spectrum, and high Q × f values of the Ba2Nd2Si4O13 and Ba2Eu2Si4O13 ceramics were attributed to their large total lattice energy and activation energy. The average bond valence of RE3+ played an important role in controlling the τf values of the Ba2RE2Si4O13 single-phase ceramics, and the high average bond valence of RE3+ corresponded with the small negative τf values. Great microwave dielectric properties (εr = 11.52, Q × f = 33,600 GHz at 11.80 GHz and τf = ‒25.6 ppm/ °C) were obtained in the Ba2Nd2Si4O13 single-phase ceramic.

The self-lubrication property of single-phase high-entropy carbide ceramic under tribo-induced effect

Self-lubricating ceramic materials are mainly achieved through the addition of lubrication phases. Although incorporating lubrication phases can improve their tribological performances, the mechanical properties are consistently compromised. Thus, designing and fabricating single-phase ceramic with favorable self-lubricity is the relentless pursuit of researchers. In this study, the single-phase high-entropy ceramic of (Hf0.2Mo0.2Nb0.2Ta0.2Ti0.2)C exhibits self-lubricating properties and which closely relates to the testing condition. The wear rate and friction coefficient decrease with the increasing of loads (not above 30 N). And the friction coefficient of (Hf0.2Mo0.2Nb0.2Ta0.2Ti0.2)C samples against Si3N4 balls is as low as 0.3 under 30 N and 5 Hz. This originates from the carbon-rich tribo-film with self-lubricity, which is generated through diffusion and enrichment under the effect of tribo-induced. Single-phase self-lubricating ceramics—using own constituent elements to form a lubricating tribo-film—are expected to open up a new research field on the high-performance friction materials.

A novel fabrication strategy of single-phase and dense CrN ceramics and its tribological behavior

Chromium nitride (CrN) is a promising structural and protective material with excellent mechanical properties and good wear and corrosion resistance. However, CrN tends to decompose into Cr2N at high temperatures, which makes the fabrication of single-phase and dense bulk CrN ceramics extremely challenging. In this work, a novel routine, ammonolysis followed by plasma activated sintering (PAS), has been proposed to fabricate single-phase and dense CrN ceramics. Single-phase CrN ceramics with a relative density of 98.2 %, higher than those in previous work, were successfully fabricated at the sintering temperature of 1200 °C. Its hardness and fracture toughness reach 11.9 GPa and 3.98 MPa m1/2, respectively, better than other CrN ceramics in literature. It exhibits friction coefficients of 0.75 to 0.45 and wear rates of 2.31 × 10−6 to 3.06 × 10−5 mm3 N−1 m−1 at the friction loads of 5–20 N. The successful fabrication of single-phase CrN ceramics can be attributed to the combined effect of the sintering atmosphere of extra N2 and rapid densification. During densification, N2 injected into the furnace will be encapsulated rapidly, creating a localized high nitrogen pressure that suppresses CrN decomposition and ultimately results in single-phase and dense CrN ceramic bulk.

Ultralow-Permittivity and Temperature-Stable Ba1-xCaxMg2Al6Si9O30 Dielectric Ceramics for C-Band Patch Antenna Applications.

Ca-substituted Ba1-xCaxMg2Al6Si9O30 ceramics were prepared to explore the relationships among their crystal structural parameters, phase compositions, dielectric properties, and coefficients of thermal expansion and applications in C-band antenna. The maximum solubility of Ba1-xCaxMg2Al6Si9O30 was located at x = 0.25, and Ba1-xCaxMg2Al6Si9O30 ceramics (0 ≤ x ≤ 0.25) crystallized in the space group P6/mcc. In Ba1-xCaxMg2Al6Si9O30 single-phase ceramics, εr was dominated by ionic polarizability and "rattling effects" of Ba2+ and Al(2)3+; Q × f was controlled by the roundness of [Si4Al2O18] inner rings and total lattice energy; and τf was affected by the bond valence of Si/Al(1)-O(1). Notably, the low average coefficients of thermal expansion (2.668 ppm/°C) at -150 °C ≤ T ≤ 850 °C and near-zero coefficients of thermal expansion (1.254 ppm/°C) at -150 °C ≤ T ≤ 260 °C were achieved for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic. Optimum microwave and terahertz dielectric properties were obtained for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic with εr = 5.80, Q × f = 31,174 at 13.99 GHz, τf = -7.10 ppm/°C, and εr = 5.71-5.85 at 0.2 THz ≤ f ≤ 1.0 THz. Also, the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic substrate had been designed as a C-band patch antenna with a high simulated radiation efficiency (87.76%) and gain (6.30 dBi) at 7.70 GHz (|S11| = -38.41 dB).

Modeling of tritium release behavior of biphasic Li2TiO3–Li4SiO4 ceramics

Biphasic Li2TiO3–Li4SiO4 ceramics have been proposed as advanced tritium breeder for solid-type breeding blankets of fusion reactors. However, the mechanism of tritium release from biphasic Li2TiO3–Li4SiO4 ceramics remains to be elucidated. In this study, an integrated numerical model for tritium release from biphasic Li2TiO3–Li4SiO4 ceramics was constructed for the first time. In the proposed model, besides the mass transfer steps for tritium release from single-phase ceramics (e.g. Li2TiO3 and Li4SiO4), a mass transfer step between the interfacial layers of Li2TiO3 and Li4SiO4 was also included to take into account the effect of two-phase interface in Li2TiO3–Li4SiO4 ceramics. By using this model, numerical simulations of tritium release from Li2TiO3–Li4SiO4 ceramics with different phase ratio and grain size were performed. The simulation results showed that the mass transfer of tritium atoms between the interfacial layers of Li2TiO3 and Li4SiO4 can effectively enhance tritium release from Li4SiO4 in biphasic Li2TiO3–Li4SiO4 ceramics. Furthermore, increasing phase ratio of Li2TiO3 and decreasing grain size of Li2TiO3 were both beneficial to tritium release from biphasic Li2TiO3–Li4SiO4 ceramics at lower temperature. The modeling work consolidated the presumption that the two-phase interface could play an important role in the tritium release process of biphasic Li2TiO3–Li4SiO4 ceramics.

Effects of Bi2O3 doping on structural and electrical properties of Ce0.8Sm0.2O1.9 electrolyte for solid oxide fuel cells

The study investigates the impact of Bi2O3 doping on the crystal structure, density, and ionic conductivity of Ce0.8Sm0.2O1.9, a type of samarium-doped ceria oxide (SDC). The material is intended for use as a solid electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFCs). The SDC-based electrolyte was created using the auto-combustion technique, with various molar ratios of Bi2O3. Phase compositions, microstructure, and ionic conductivity of all ceria ceramics were analysed using XRD, SEM and impedance analyses, respectively. The language is formal, clear, objective, and value-neutral, using high-level, standard language with consistent technical terms. Grammar, spelling, and punctuation are correct. Consistent citation and footnote style are maintained. The samples are single-phase ceramics that crystallise into a cubic fluorite type structure with space group Fm-3 m, as confirmed by the X-ray diffraction pattern. Technical abbreviations are explained. The structure ensures a logical flow of information with causal connections between statements. No filler words or biased language are used. SDC/Bi2O3 composite powders exhibit high sintering activity. The relative density of all samples sintered at 1300 ºC for 5 h was more than 96%, which is higher than that achieved by pure SDC electrolyte sintered at 1400 ºC (94.06%). Electrochemical performance results demonstrate that adding an appropriate amount of Bi2O3 can significantly enhance the conductivity of SDC materials. The SDC-based electrolyte containing 9 mol% of Bi2O3 (SDCB9) demonstrates the maximum conductivity of 43.5 mS·cm−1 at 800 °C, surpassing that of pure SDC which measures 26.86 mS·cm−1.

Structure characteristics and microwave/terahertz dielectric response of low-permittivity (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 high-entropy ceramics

Microwave dielectric ceramics play a vital role in wireless communication systems. However, it is a great challenge to obtain ideal performances of single-phase ceramics. In this work, (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 (abbreviated as L5ZMO) high-entropy ceramics were successfully prepared by the solid-state reaction method, the pure trigonal L5ZMO structure can be synthesized in the mixture calcined at 700 °C. Rietveld refinement based on XRD data reveals that lattice parameters of L5ZMO ceramics are affected by the radius of the five rare earth elements, which indicates that the rare earth elements have been solubilized and randomly distributed in the Ln-site. The relative density illustrates a strong dependence on sintering temperature, which gradually increases with increasing sintering temperature. Based on the analysis of bond characteristics, the Mo–O bond exhibits a vital effect on the dielectric properties of L5ZMO ceramics. Besides, the infrared reflection spectrum and terahertz time-domain spectroscopy analysis show that ionic polarization is the dominant polarization in the microwave/terahertz bands. Meanwhile, the tan δ can be further reduced by optimizing process parameters. Notably, the L5ZMO high-entropy ceramics sintered at 750 °C exhibit outstanding dielectric properties of εr = 10.46, Q·f = 59,713 GHz, and τf = −21.94 ppm/°C, indicating that the high-entropy design optimizes τf (−38.8 ppm/°C) of the simple La2Zr3(MoO4)9 ceramics. The attempt provides theoretical guidance for the application of high-entropy design concepts in microwave/terahertz bands.

Study of Gas Swelling Processes under Irradiation with Protons and He2+ Ions in Li4SiO4–Li2TiO3 Ceramics

One of the important areas of research in the energy sector is the study of the prospects for using new types of nuclear fuel, including tritium, which is one of the most promising types of fuel for thermonuclear energy. At the same time, for the production of tritium in the required quantities, the one that is the most optimal is the use of blanket materials based on lithium-containing ceramics. This is where tritium is released from lithium under the influence of neutron irradiation. The paper presents the results of an investigation of the influence of two-phase ceramics based on Li4SiO4–Li2TiO3 compounds on the resistance to external influences (mechanical loads) during the accumulation of hydrogen and helium (He2+) in the near-surface layer. The interest in such studies is primarily related to the search for solutions in the field of creating high-strength materials for tritium generation for its further use as nuclear fuel for thermonuclear fusion, as well as to the study of the mechanisms of the influence of different phases on the changes in the strength properties of ceramics, which provides an opportunity to expand fundamental knowledge in this area. The proposed method of obtaining two-phase ceramics by mechanical-chemical mixing and subsequent sintering into spherical particles enables the production of well-structured, high-strength ceramics of specified geometric dimensions (limited only by the dimensions of the mold) with a controlled phase ratio. During the experiments, it was found that increasing the content of Li4SiO4 phase in ceramics leads to an increase in strength characteristics (hardness, resistance to cracking) by 15–20% compared to single-phase ceramics. The most optimal composition of two-phase ceramics with high resistance to destructive embrittlement is the ratio of phases 0.75Li4SiO4–0.25Li2TiO3. One of the factors explaining the increase in resistance to destructive embrittlement under high-dose irradiation for two-phase ceramics is the increased dislocation density and the presence of interphase or intergranular boundaries, the high concentration of which leads to the creation of additional obstacles to the agglomeration of hydrogen and helium in the near-surface layer.

Phase evolution and microware dielectric properties of high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics

In this study, high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics were synthesized by solid-state reaction method. The raw materials gradually formed spinel aluminates from 700 to 1400 °C and finally formed high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics after calcination at 1400 °C for 4 h. The high-configuration entropy and low average atomic-size difference were beneficial to form single-phase high-entropy ceramics. Partial lattice distortion occurred within the high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics structure, and its grain size gradually increased with increasing sintering temperature. The high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics exhibited good microwave dielectric properties when sintered at 1550 °C for 4 h: dielectric constant (εr) = 7.4, quality factor (Qf) = 58,200 GHz, and temperature coefficient of resonance frequency (τf) = –64 ppm/°C. The εr values were mainly affected by the dielectric polarizability. The Qf values were highly related to the relative density and covalency of A-site bond, whereas the τf values closely depended on the bond strength of A-site.

Formation mechanism and high-temperature self-lubricating behavior of (HfMoNbTaTi)C system single-phase high-entropy ceramics

Formation mechanism and high-temperature self-lubricating behavior of (HfMoNbTaTi)C system single-phase high-entropy ceramics

Dense and single-phase KTaO3 ceramics obtained by spark plasma sintering

Potassium tantalate (KTaO3) is a promising material for dielectric applications at low temperature. However, dense and single-phase ceramics cannot be obtained by conventional sintering because of the evaporation of potassium that leads to secondary phases. Here, we demonstrate that spark plasma sintering is a suitable method to obtain dense and single-phase KTaO3 ceramics, by optimizing three parameters: initial composition, temperature, and pressure. A 2 mol% K-excess in the precursors leads to a large grain growth and dense single-phase ceramics. Without K-excess, a small amount of secondary phase (K6Ta10.8O30) is observed at the surface but can be removed by polishing. At ∼10 K, the dielectric permittivity is 4 times higher in the ceramic from the 2 mol% K-excess powder, because of the larger grain size. The thermal conductivity decreases with decreasing grain size and stays above the thermal conductivity of KNbO3 ceramics.

Analysis of structural and electrical properties of Sn modified Ca0.6Sr0.4TiO3 ceramics

In this study, we synthesized Ca0.6Sr0.4Ti1-xSnxO3 ceramics using the solid-state reaction technique, varying the Sn compositions from x = 0.0 to 0.08. X-ray diffraction analysis revealed a slight modification in the crystallographic structure of calcium strontium titanate (CST) as the Sn content increased, while confirming the formation of single-phase ceramics. Parameters such as crystallite size, lattice strain, stacking fault, and dislocation density were estimated based on the XRD data. Crystallite size generally increased with higher tin concentrations, except for x = 0.08 where a decrease was observed. The FTIR spectra exhibited a broad band, and deconvolution using a Gaussian distribution was employed to identify structural units. Density measurements demonstrated densification with increasing Sn content. The activation energy values increased from 0.76 eV for undoped CST to 0.95 eV for x = 0.06, except for x = 0.08, which measured 0.89 eV, indicating the role of Sn in modifying the structure. Activation energy was determined through linear fitting of experimental data, revealing that the reciprocal temperature dependence of DC conductivity followed Arrhenius behaviour. These findings contribute novel insights into the synthesis and characterization of Ca0.6Sr0.4Ti1-xSnxO3 ceramics, highlighting the impact of Sn on the structural and electrical properties of CST.

Microstructure, mechanical and tribological properties of high-entropy (TaTiVW)C4 ceramics

High-entropy ceramics (HEC) with a fixed composition of (TaTiVW)C4 were prepared by spark plasma sintering (SPS) from 1600 °C to 2100 °C. Furthermore, the influence of temperature on microstructure, mechanical and tribological properties are systematically investigated. The results reveal that single-phase and dense (TaTiVW)C4 ceramics are formed at the temperature of 1700 °C. The metal elements in (TaTiVW)C4 ceramics are evenly distributed after sintering at a high temperature (2100 °C), whereas the pores are enriched with oxygen impurities. The fracture toughness of (TaTiVW)C4 ceramics, sintered at ≥1900 °C, is found to be higher than 5 MPa·m1/2, which can be ascribed to the crack deflection. (TaTiVW)C4 ceramics also exhibit excellent wear resistance with an average specific wear rate (WRs) of 2 × 10−6 mm3·N−1·m−1. The formation of tribo-oxide layer (Ta2O5, TiO2, V2O5, WO3) was conducive to the reduction of friction and wear. The relatively low synthesis temperature and excellent wear resistance make (TaTiVW)C4 a potential wear-resistant material.

Phase-Field Simulation of Temperature-Dependent Thermal Shock Fracture of Al2O3/ZrO2 Multilayer Ceramics with Phase Transition Residual Stress.

Compared with single-phase ceramics, the thermal shock crack propagation mechanism of multiphase layered ceramics is more complex. There is no experimental method and theoretical framework that can fully reveal the thermal shock damage mechanism of ceramic materials. Therefore, a multiphase phase-field fracture model including the temperature dependence of material for thermal shock-induced fracture of multilayer ceramics is established. In this study, the effects of residual stress on the crack propagation of ATZ (Al2O3-5%tZrO2)/AMZ (Al2O3-30%mZrO2) layered ceramics with different layer thickness ratios, layers, and initial temperatures under bending and thermal shock were investigated. Simulation results of the fracture phase field under four-point bending are in good agreement with the experimental results, and the crack propagation shows a step shape, which verifies the effectiveness of the proposed method. With constant thickness, high-strength compressive stress positively changes with the layer thickness ratio, which contributes to crack deflection. The cracks of the ceramic material under thermal shock have hierarchy and regularity. When the layer thickness ratio is constant, the compressive residual stress decreases with the increase in the layer number, and the degree of thermal shock crack deflection decreases.

Self-lubrication of single-phase high-entropy ceramic enabled by tribo-induced amorphous carbon

Designing single-phase ceramics with favorable self-lubricity is a substantial challenge due to the strong chemical bonds and difficulty to shearing. Most conventional lubricating ceramics only benefit from adding solid lubricants, which largely limits the mechanical properties of the resulting materials. Here, we report a single-phase ceramic inspired by the novel high-entropy design concept and tribo-induced effect, and which can achieve an outstanding self-lubricity (friction coefficient is as low as 0.1) at 200–400 °C in a vacuum environment. The self-lubricity is attributed to two factors, namely the decomposition of the (Hf-Mo-Nb-Ta-Ti)C ceramic leading to formation of the amorphous carbon film at the sliding interfaces, and the diffusion of carbon atom under the effect of high-temperature tribo-induced enabling easy shear contact. Based on the experimental and theoretical findings, we formulate a novel design strategy for single-phase self-lubricating ceramics by in-situ forming lubricating phase.

Degree of inversion of A/B lattice sites and microwave/millimeter wave/terahertz dielectric properties of MgAl2-x(Zn0.5Mn0.5)xO4 ceramics

In this work, spinel-structured MgAl2-x(Zn0.5Mn0.5)xO4 (0 ≤ x ≤ 0.08) single-phase ceramics were prepared through a solid-state reaction route. The substitution of (Zn0.5Mn0.5)3+ for Al3+ at the octahedral site affected the degree of inversion of A/B lattice sites, bond length/strength/valence, and covalency of metal-oxygen bond in the tetrahedron and hence microwave dielectric properties of MgAl2O4. The variation in εr and tanδ of ceramics is investigated in the millimeter wave-terahertz frequency band by combining infrared reflection spectrum and terahertz time-domain spectroscopy. A high Q×f value of 111,010 GHz @ 12.01 GHz, low εr = 8.3, and slightly lower τf = −60 ppm/°C is obtained for MgAl1.98Zn0.01Mn0.01O4 ceramics, which is tuned by adding a small amount of SrTiO3. The composite ceramics exhibited a near-zero τf (2.8 ppm/°C), high Q×f (55,400 GHz @ 11.15 GHz), and low εr (= 8.5), showing a great potential application prospect for 5G/6G wireless communication.

Single-phase formation mechanism and dielectric properties of sol-gel-derived Ba(Ti0.2Zr0.2Sn0.2Hf0.2Ce0.2)O3 high-entropy ceramics

• Single-phase BTZSHC high-entropy ceramics were successfully prepared via the sol-gel method at relative low temperature. • The single-phase formation mechanism of the as-prepared high-entropy ceramics is attributed to thermodynamic factors. • The sluggish diffusion effect ensures the thermal stability of high-entropy systems. • The relaxor behavior of the BTZSHC high-entropy ceramics is caused by the thermal evolution of the PUs in the lattice. Single-phase Ba(Ti 0.2 Zr 0.2 Sn 0.2 Hf 0.2 Ce 0.2 )O 3 (BTZSHC) high-entropy ceramics (HECs) with the perovskite structure were successfully prepared via the sol-gel method. The results reveal that the as-prepared ceramics exhibit a single cubic phase belonging to the P m 3 ¯ m space group. The high entropy is the driving force of the formation of single-phase ceramics. A larger entropy (Δ S mix ) and a negative enthalpy (Δ H mix ) are conducive to the formation of single-phase compounds. Herein, Δ S mix = 0.323 R mole –1 and Δ H mix = −43.88 kJ/mol. The sluggish-diffusion effect ensures the thermal stability of high-entropy systems. Dielectric measurements reveal that the as-prepared BTZSHC high-entropy ceramics are relaxor ferroelectrics, and the degree of relaxor ( γ ) is 1.9. The relaxor behavior of the as-prepared ceramics can be ascribed to the relaxation and thermal evolution of their polar units (PUs). The findings of this work provide a theoretical basis and technical support for the preparation of single-phase high-entropy ceramics.

Microstructural evolution of Si(HfxTa1−x)(C)N polymer-derived ceramics upon high-temperature anneal

Ultra-high temperature ceramic nanocomposites (UHTC-NC) within the Si(HfxTa1−x)(C)N system were synthesized via the polymer-derived ceramics (PDC) synthesis route. The microstructure evolution of the materials was investigated upon pyrolysis and subsequent heat treatment. The crystallization behavior and phase composition were studied utilizing X-ray diffraction, scanning- and transmission electron microscopy. Single-source-precursors were converted into amorphous single-phase ceramics, with the exception of surface crystallization effects, at 1000 °C in NH3. Annealing in N2 at 1600 °C resulted in fully crystalline UHTCs. The powder samples revealed microstructures consisting of two characteristic regions, bulk and surface; displaying intrinsic microstructure and phase composition differences. Instead of the expected nitrides, transition metal carbides (TMC) were detected upon high-temperature anneal. The residual carbon available in the system triggered a decomposition reaction, resulting in the formation of TMCs plus gaseous nitrogen and SiC. Experimental data underline that N-containing PDCs are prone to phase separation accompanied by thermal decomposition and diffusion-controlled coarsening.