An antipolar phase is confirmed for NaNbO3 thin films grown by pulsed laser deposition on SrTiO3 (100) substrates. Reciprocal space maps and transmission electron microscopy reveal the presence of characteristic 1/4 superlattice reflections, indicative of the antipolar displacement of Na and Nb-ions. Furthermore, x-ray diffraction unveils the presence of two different orientations of the same phase for thin films beyond a critical thickness of about 60 nm. This orientation change with increasing thickness can be explained as an extraordinary strain compensation mechanism, changing magnitude and sign of the strain at the same time. The polarization vs electric field behavior exposes a characteristic thickness dependence, with the antiferroelectric phase stabilized for very thin films and a field induced ferroelectric hysteresis for a film of 310 nm having a maximum polarization of 26.5  μC [Formula: see text], which is among the highest values reported for NaNbO3 thin films grown on SrTiO3 (100).

SiBN ceramics are widely considered to be the most promising material for microwave-transparent applications in harsh environments owing to its excellent thermal stability and low dielectric constant. This work focuses on the synthesis and ceramization of single-source precursors for the preparation of SiBN ceramics as well as the investigation of the corresponding microstructural evolution at high temperatures including molecular dynamic simulations. Carbon- and chlorine-free perhydropolysilazanes were reacted with borane dimethyl sulfide complex at different molar ratios to synthesize single-source precursors, which were subsequently pyrolyzed and annealed under N2 atmosphere (without ammonolysis) to prepare SiBN ceramics at 1100, 1200, and 1300 °C with high ceramic yield in contrast to previously widely-used ammonolysis synthesis process. The obtained amorphous SiBN ceramics were shown to have remarkably improved thermal stability and oxidation resistance compared to amorphous silicon nitride. Particularly, the experimental results have been combined with molecular dynamics simulation to further study the amorphous structure of SiBN and the atomic-scale diffusion behavior of Si, B, and N at 1300 °C. Incorporation of boron into the Si—N network is found to suppress the crystallization of the formed amorphous silicon nitride and hence improves its thermal stability in N2 atmosphere.

A facile and eco‐friendly strategy is presented for synthesizing novel nanocomposites, with MoP quantum dots (QDs) as cores and graphitic carbon as shells, these nanoparticles are dispersed in a nitrogen and phosphorus‐doped porous carbon and carbon nanotubes (CNTs) substrates (MoP@NPC/CNT). The synthesis involves self‐assembling reactions to form single‐source precursors (SSPs), followed by pyrolysis at 900 °C in an inert atmosphere to obtain MoP@NPC/CNT‐900. The presence of carbon layers on the MoP QDs effectively prevents particle aggregation, enhancing the utilization of active MoP species. The optimized sample, MoP@NPC/CNT‐900, exhibits remarkable electrocatalytic activity and durability for the hydrogen evolution reaction (HER). It demonstrates a low overpotential of 155 mV at 10 mA cm−2, a small Tafel slope of 76 mV dec−1, and sustained performance over 20 hours in 0.5 M H2SO4. Furthermore, the catalyst shows excellent activity in 1 M KOH, with a relatively low overpotential of 131 mV and long‐term durability under constant current input. The exceptional HER activity can be attributed to several factors: the superior performance of MoP QDs, the large surface area and good conductivity of the carbon substrates, and the synergistic effect between MoP and carbon species.

Carbon supported metallic nanomaterials are of great interest due to their low-cost, high durability and promising functional performance. Herein, a highly active oxygen evolution reaction (OER) electrocatalyst comprised of defective carbon shell encapsulated metal (Fe, Co, Ni) nanoparticles and their alloys supported on in-situ formed N-doped graphene/carbon nanotube hybrid is synthesized from novel single-source-precursors (SSP). The precursors are synthesized by a facile one-pot reaction of tannic acid with polyethylenimine and different metal ions and subsequent pyrolysis of the SSP. Benefiting from the heteroatom doping of carbon and formation of wellencapsulated metal/alloy nanoparticles, the obtained FeNi@NC-900 catalyst possesses lowest overpotentials of 310 mV to achieve a current density of 10 mA cm À 2 for OER with a small Tafel slope value of 45 mV dec À 1 , indicating excellent catalytic performance due to the following features: (1) A synergistic electronic effect among metal alloy nanoparticles, nitrogendoped carbon, and entangled carbon nanotubes; (2) penetration of electrolyte is promoted towards the active sites through the porous structure of the formed mesoporous carbon clusters;(3) the unique core-shell nanostructure of the hybrid material effectively curbs the degradation of electrocatalyst by protecting the alloy nanoparticles from harsh electrolyte. This work advances an inexpensive and facile method towards the development of transition metal-based hybrid material for potential energy storage and conversion.

In the present work, bulk Si3N4/HfBxN1‐x ceramic nanocomposites were successfully fabricated via a polymer‐derived ceramic approach. The chemical reaction to form the single‐source precursor was confirmed by FT‐IR and XPS, in which both Si−H and N−H groups of perhydropolysilazane react with borane dimethyl sulfide complex and tetrakis(dimethylamido) hafnium(IV). The investigation of the polymer‐to‐ceramic transformation of the synthesized precursors indicates that Hf‐ and B‐modified PHPS exhibits high ceramic yields of up to 100 wt % after pyrolysis at 1000 °C under ammonia. Moreover, XRD and TEM results show that the SiHfBN ceramics with a molar ratio of B : Hf=5 and 10 resist crystallization at temperatures up to 1500 °C and separate after annealing at 1700 °C into nanocomposites comprising of an α‐Si3N4 matrix with embedded ternary HfBxN1‐x phases, solid solutions of rock salt‐type HfN and HfB. Based on the investigation, warm‐pressing was applied to fabricate bulk SiHfBN specimens, and the oxidation behavior of samples annealed at 1700 °C was recorded at 1500 °C over a range of oxidation times between 1 and 50 h. The weight changes of Si3N4/HfBxN1‐x ceramics with B : Hf molar ratios of 2 : 1, 5 : 1 and 10 : 1 are 4.31 %, 4.37 % and 2.57 %, respectively. The formation of HfSiO4, B2O3 and SiO2 during oxidation plays a crucial role for the improvement of the oxidation resistance of the Si3N4/HfBxN1‐x ceramics.