Electronic band structures of two novel semiconducting nitrides of the group-IV elements of Th3P4-type crystal structure, c-M3N4, where M[DOUBLE BOND]Zr or Hf, is investigated using an element specific soft X-ray spectroscopy for the first time. From the pairs of N 1s X-ray absorption and N 2p [RIGHTWARDS ARROW] 1s resonant X-ray emission spectra partial densities of states (PDOS) of nitrogen, predicted to be strongly hybridized with those of the metals, are obtained for both compounds. From these data the electronic band gaps of oxygen bearing c-Zr3N4 and of c-Hf3N4, predicted before to be direct or nearly direct, are derived to be Eg = 1.6 eV and Eg = 1.8 eV, respectively. While the experimentally determined Eg for c-Hf3N4 agrees with the theoretical one obtained using the local density approximation (LDA) method, the Eg measured for oxygen bearing c-Zr3N4 is significantly higher than those calculated using both the LDA and the generalized gradient approximation method. The examined compounds, having high hardness, elastic moduli and oxidation resistance, appear to be multifunctional materials suitable also for applications as (opto)electronic materials. Band gap evolution in c-M3N4 nitrides as a function of the cation type, Zr or Hf

PtAs2 appears to be the least compressible known arsenide with a bulk modulus of 220(5) GPa and a shear modulus of between 64 and 77 GPa. PtAs2 has a hardness of 11(1) GPa, which is remarkably high for an arsenide. These elastic and mechanical properties in combination with the known chemical inertness and the small indirect band gap add interest to the use and occurrence of PtAs2 at Pt-GaAs contacts in transistors. We note the modest fracture toughness of 1.1–1.6 MPa m1/2 of PtAs2.

During a ballistic impact, the protective material that plays the role of armour has to dissipate the kinetic energy in order to limit the projectile penetration in the target. Our aim is to emphasis on the role played by a liquid-filled system on the impact energy mitigation due to cavitation inception and later bubble expansion. To observe this, small scale experiments have been carried out on a three layers sample (Aluminium-Water-PMMA) submitted to shock waves induced by laser impact applied on the Al face. Rapid camera visualizations allow reproducing, at small scale, the effects of projectiles on armours for various monitored impact energies. We observe the formation of bubbles for sufficiently intense impacts due to traction effects in the water caused by the multiple reflections of waves within the sample. The cavitation threshold of water under dynamic loading is then experimentally investigated for two samples: one with 600 μm thick Al / 400 μm of water and 3 mm of PMMA, the other with 1000 μm thick Al / 1600 μm of water and 3 mm of PMMA. Using dimensional analysis, we show that the energy taken during the process of inception and bubble expansion becomes more important as the energy of the impact increases.

Nanoindentation testing was used to determine elastic moduli and hardness of η-Ta2N3, a novel stiff and hard high-pressure compound recoverable at ambient conditions. For a sample having porosity of 14% we confirmed densification of its upper layer induced by mechanical polishing: At depths we obtained higher reduced elastic modulus and higher hardness when compared with the sample without the densified layer. Using the experimental values of and of porosity we derived the shear modulus of dense η-Ta2N3 to be . Hardness of the porous η-Ta2N3 was measured to be 18 GPa and its fracture toughness estimated to exceed . The Pugh criterion suggests a high malleability of η-Ta2N3 which could explain the observed surface densification.

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