We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr₂O₄ nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr₂O₄ nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10⁻⁴ at a frequency of 1 Hz. Nanoparticulate ZnCr₂O₄-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

In this work we present a detailed study showing the importance of the Kubelka-Munk (KM) correction in the analysis of diffuse reflectivity measurements to characterize spin crossover compounds. Combined reflectance and magnetic susceptibility measurements are carried out as a function of temperature or time to highlight the conditions under which this correction becomes critical. In particular, we investigate the influence of the color contrast between the two spin states on the reflectance measurements. Interestingly, the samples’ contrast seems to play an important role on the spin-like domain structure as suggested by the symmetry of the FORC diagrams. These latest results are discussed within the framework of Classical Preisach model (CPM).

This research evaluates the compounding, processing, and performance of a sustainable biocomposite filament for additive manufacturing, utilizing poly(lactic acid) (PLA) filled with raw pine cone (Pinus sylvestris) flour at 5 and 10 wt% filler contents. Tensile properties, surface topography, and processability of extruded filaments and 3D-printed specimens were systematically investigated. Incorporating pine cone flour yielded unprinted filament tensile strengths of 21.06 MPa (5 wt%) and 18.51 MPa (10 wt%), while 3D-printed specimens retained ~85% (5 wt%) and ~79% (10 wt%) of their corresponding unprinted composite filament tensile strength. This reduction in strength is hypothesized to stem from weak interfacial adhesion and polarity mismatch between the hydrophobic PLA and hydrophilic biomass, which is suggested to promote micro-void formation. Topographical analysis revealed surface anisotropy: top surface roughness increased ($Ra$ up to 9.85 µm; $Sz$ up to 100.2 µm), likely influenced by melt viscosity, whereas lateral roughness decreased ($Ra$ down to 3.10 µm; $Sz$ down to 45.4 µm), potentially associated with suppressed die swell. Printed ductility increased (>8%), a trend attributed to potential inter-layer re-melting during deposition. To overcome limited interfacial bonding, future work should incorporate coupling agents or chemical surface modifications. Overall, among the evaluated formulations, the composite with 5 wt% filler demonstrates a favorable balance of processability, mechanical integrity, and surface quality, showing high potential for non-load-bearing prototypes, indoor decorative elements, and light-duty packaging.