The Principle of Maximal Simplicity for Modular Inorganic Crystal Structures

Modularity is an important construction principle of many inorganic crystal structures that has been used for the analysis of structural relations, classification, structure description and structure prediction. The principle of maximal simplicity for modular inorganic crystal structures can be formulated as follows: in a modular series of inorganic crystal structures, the most common and abundant in nature and experiments are those arrangements that possess maximal simplicity and minimal structural information. The latter can be quantitatively estimated using information-based structural complexity parameters. The principle is applied for the modular series based upon 0D (lovozerite family), 1D (biopyriboles) and 2D (spinelloids and kurchatovite family) modules. This principle is empirical and is valid for those cases only, where there are no factors that may lead to the destabilization of simplest structural arrangements. The physical basis of the principle is in the relations between structural complexity and configurational entropy sensu stricto (which should be distinguished from the entropy of mixing). It can also be seen as an analogy of the principle of least action in physics.

Pengaruh lama maturasi pada sintesis biokeramik komposit CaO-TiO2 terhadap ukuran kristal, mikrostruktur dan kekerasan

Perkembangan Ilmu Pengetahuan dan Teknologi (IPTEK) akhir-akhir ini mendorong banyaknya inovasi dalam dunia medis terutama penggunaan biomaterial sebagai implan pengganti tulang dan gigi, salah satunya bahan tersebut adalah biokeramik komposit CaO-TiO2. Bahan biokeramik komposit CaO-TiO2 dapat digunakan untuk memperbaiki bagian tubuh yang rusak terutama sebagai implan gigi, penyambung tulang, struktur penahan katup jantung, dan pengganti tulang tengkorak. Paduan antara CaO-TiO2 memiliki beberapa keuntungan diantaranya memiliki biokompatibilitas yang baik, dapat tumbuh serta berkembang bersama-sama dengan tulang asli serta memiliki ketahanan mekanik yang baik. Berdasarkan paparan di atas, tujuan dari penelitian ini adalah mengetahui pengaruh lama maturasi pada biokeramik komposit CaO-TiO2 dengan metode kopresipitasi terhadap kristalinitas, mikrostruktur, dan kekerasan. Pada penelitian ini bahan dasar yang digunakan adalah CaO yang berasal dari batuan kapur alam yang diambil dari pantai Balekambang Kabupaten Malang dan TiO2 dengan kemurnian 99 persen. Sampel dilarutkan dalam aquades dan distirer selama 15 jam pada suhu 70 derajat celcius. Lama maturasi divariasi mulai dari 12, 24, 36, 48, dan 60 jam, dianneling pada suhu 100 derajat celcius selama 24 jam dan disintering selama 4 jam pada suhu 1100 derajat celcius. Sampel dikarakterisasi ukuran kristal, mikrostruktur, dan kekerasan, dengan menggunakan XRD, SEM, dan Micro Vickers Hardness. Hasil analisis CaO-TiO2 menunjukkan kecocokan dan keberhasilan sintesis dengan model pembanding CaO-TiO2 dari Inorganic Crystal Structure Database (ICSD) dengan nilai score diatas 50. Berdasarkan perhitungan teoritik yang dilakukan dengan menentukan nilai FWHM (Full Widht at Half Maximum) dari pola difraksi sampel yang kemudian digunakan pada formula scherrer, diperoleh hasil peningkatan ukuran kristal yang bervariasi terhadap lama maturasi komposit CaO-TiO2 dengan besar antara 45,06 nm-70,85 nm. Dengan meningkatnya ukuran kristal terhadap lama maturasi maka akan disertai oleh peningkatan ukuran butir, sehingga semakin sedikit jumlah pori-pori yang terbentuk pada bahan yang ditunjukan oleh menurunnya nilai luas fraksi pori sebesar 4,97 persen pada lama maturasi 12 jam menjadi 4,79 persen pada lama maturasi 60 jam. Dengan semakin kecilnya nilai fraksi total pori maka semakin besar kekerasan dari bahan tersebut, hal ini ditunjukan dengan nilai kekerasan tertinggi diperoleh pada lama maturasi 60 jam sebesar 497,2 MPa.

Geometrical prediction of cleavage planes in crystal structures

Cleavage is the ability of single crystals to split easily along specifically oriented planes. This phenomenon is of great interest for materials' scientists. Acquiring the data regarding cleavage is essential for the understanding of brittle fracture, plasticity and strength, as well as for the prevention of catastrophic device failures. Unfortunately, theoretical calculations of cleavage energy are demanding and often unsuitable for high-throughput searches of cleavage planes in arbitrary crystal structures. A simplified geometrical approach (GALOCS = gaps locations in crystal structures) is suggested for predicting the most promising cleavage planes. GALOCS enumerates all the possible reticular lattice planes and calculates the plane-average electron density as a function of the position of the planes in the unit cell. The assessment of the cleavage ability of the planes is based on the width and depth of planar gaps in crystal structures, which appear when observing the planes lengthwise. The method is demonstrated on two-dimensional graphene and three-dimensional silicon, quartz and LiNbO3 structures. A summary of planar gaps in a few more inorganic crystal structures is also presented.

Complexity Parameters for Molecular Solids

Structural complexity measures based on Shannon information entropy are widely used for inorganic crystal structures. However, the application of these parameters for molecular crystals requires essential modification since atoms in inorganic compounds usually possess more degrees of freedom. In this work, a novel scheme for the calculation of complexity parameters (HmolNet, HmolNet,tot) for molecular crystals is proposed as a sum of the complexity of each molecule, the complexity of intermolecular contacts, and the combined complexity of both. This scheme is tested for several molecular crystal structures.

Crystal structure of silver carbonate iodide Ag10(CO3)3I4

The title silver carbonate iodide, Ag10(CO3)3I4, decasilver(I) tris(carbonate) tetraiodide, was recently reported as a precursor of the new superionic conductor Ag17(CO3)3I11. Ag10(CO3)3I4, was prepared by heating a stoichiometric powder mixture of AgI and Ag2CO3 at 430 K. A single-crystal suitable for X-ray diffraction analysis was obtained by slow cooling of a melt with an AgI-rich composition down from 453 K. Ag10(CO3)3I4 exhibits a layered crystal structure packed along [10\overline{1}], in which Ag atoms are intercalated between the layers of hexagonally close-packed I atoms, and CO3 groups. Up to now, Cs3Pb2(CO3)3I is the only other compound containing carbonate groups and iodide ions registered in the Inorganic Crystal Structure Database.

The Future Role of Inorganic Crystal Scintillators in Dark Matter Investigations

Crystal scintillators and in particular inorganic scintillators play an important role in the investigation of Dark Matter (DM) and other rare processes. The investigation of a DM signature, as the annual modulation, or the directionality technique requires the use of highly radiopure detectors able to explore the very low energy region maintaining a high stability of the running conditions. In this paper, the cases of NaI(Tl), ZnWO4 and SrI2(Eu) crystal scintillators are described in the framework of our activities at the Gran Sasso National Laboratory of the INFN. Their role, the obtained results in DM investigation, as well as their potential and perspectives for the future are reviewed.

Techniques for Background Identification in the Search for Rare Processes with Crystal Scintillators

In astroparticle, nuclear and subnuclear physics, low-counting experiments play an increasingly important role in the investigation of rare processes such as dark matter, double beta decay, some neutrino processes and low-background spectrometry. Extremely low-background features are more and more required to produce detectors and apparata of suitable sensitivity. Over time, a great deal of interest and attention in developing experimental techniques suitable to improve, verify and maintain the radiopurity of these detectors has arisen. In this paper, the characterization of inorganic crystal scintillators (such as, e.g., NaI(Tl), ZnWO4 and CdWO4) using α, β and γ radioactive sources and the main experimental techniques applied in the field to quantitatively identify the radioactive contaminants are highlighted; in particular, we focus on inorganic crystal scintillators, widely used in rare processes investigation, considering their applications at noncryogenic temperatures in the framework of the DAMA experiment activities at the Gran Sasso National Laboratory of the INFN (National Institute for Nuclear Physics, INFN).