Crystals

Two-dimensional (2D) powders constitute an important class of molecular thin films where a specific close-packed plane forms parallel to the substrate surface, while there is no preferred lateral ordering. Using results from classic lattice reduction theory, a systematic scheme is proposed in order to determine the 3D surface unit cell for 2D powders in reciprocal space. The approach is based on a sorted set of lengths of the in-plane components of the scattering vector, which is directly obtained from the scattering pattern. After a first match is established, a refinement procedure is presented that makes full use of the complete set of scattering vectors and, as such, corrects for small experimental errors and ensures a good overall match with the observed reflections. After identifying the in-plane components, the full 3D surface unit cell can be found in a straightforward way.

Blue calcite mineral formations occurring within Paleozoic marbles of Central Anatolia have been investigated in terms of their mineralogical and geochemical characteristics, as well as their potential for use as ornamental stones or decorative objects. XRD analyses of samples with different color tones (white, grayish-blue, and blue) revealed that the white sample contains only calcite, the grayish-blue samples include calcite and dolomite, while the blue sample contains calcite and quartz. XRF and ICP-MS analyses indicate a marked enrichment of trace elements such as Fe, Cr, and Ni in the blue sample, and Mn and Fe in the grayish-blue samples, suggesting these elements may influence the observed color variations. The presence of dolomite in grayish-blue samples and quartz in the blue sample corresponds to elevated MgO and SiO₂ contents, respectively. Based on their distinct colors, textures, transparency, and other aesthetic properties, the grayish-blue and blue marbles show significant potential for use as decorative stones or ornamental objects.

An attractive cryogenic near-zero thermal expansion (ZTE) behavior was achieved in the Mn₃Cu_0.5Ge_0.5N_0.78C_0.22 compound, spanning a broad temperature window of 120 K (5 K to 125 K) with an average coefficient of thermal expansion (CTE) of α = 0.68 × 10⁻⁶ K⁻¹. Furthermore, the effect of sintering temperature and holding time on thermal expansion and magnetic properties were investigated. Two distinct magnetic phase transitions are evident in the magnetization–temperature (M-T) curve of Mn₃Cu_0.5Ge_0.5N_0.78C_0.22, which precede the near-ZTE behavior. These two antiferromagnetic (AFM)-like ordering transitions are hypothesized to play a pivotal role in governing the ZTE behavior, as they induce two episodes of negative thermal expansion (NTE). The realization of ZTE behavior is thus attributed to the counterbalance of these two NTE contributions, which can be effectively tuned by varying the carbon content or optimizing the sintering process parameters. Collectively, these results demonstrate significant potential for the design of diverse cryogenic functional materials.