ABSTRACT
Lightweight diamond-like structure (DLS) materials are excellent candidates for thermoelectric (TE) applications due to their low costs, eco-friendly nature, and property stability. The main obstacles restricting the energy-conversion performance by the lightweight DLS materials are high lattice thermal conductivity and relatively low carrier mobility. By investigating the anion substitution effect on the structural, microstructural, electronic, and thermal properties of Cu2CoSnS4-xSex, we show that the simultaneous enhancement of the crystal symmetry and bonding inhomogeneity engineering are effective approaches to enhance the TE performance in lightweight DLS materials. Particularly, the increase of x in Cu2CoSnS4-xSex makes the DLS structure with the ideal tetrahedral bond angles of 109.5° favorable, leading to better crystal symmetry and higher carrier mobility in samples with higher selenium content. In turn, the phonon transport in the investigated DLS materials is strongly disturbed due to the bonding inhomogeneity between anions and three sorts of cations inducing large lattice anharmonicity. The increase of Se content in Cu2CoSnS4-xSex only intensified this effect resulting in a lower lattice component of the thermal conductivity (κL) for Se-rich samples. As a result of the enhanced power factor S2ρ-1 and the low κL, the dimensionless thermoelectric figure of merit ZT achieves a high value of 0.75 for Cu2CoSnSe4 DLS material. This work demonstrates that crystal symmetry and bonding inhomogeneity play an important role in the transport properties of DLS materials and provide a path for the development of new perspective materials for TE energy conversion.
ABSTRACT
Uncovering of the origin of intrinsically low thermal conductivity in novel crystalline solids is among the main streams in modern thermoelectricity. Because of their earth-abundant nature and environmentally friendly content, Cu-based thiospinels are attractive functional semiconductors, including thermoelectric (TE) materials. Herein, we report the crystal structure, as well as electronic and TE properties of four new Cu2MHf3S8 (M-Mn, Fe, Co, and Ni) thiospinels. The performed density functional theory calculations predicted the decrease of the band gap and transition from p- to n-type conductivity in the Mn-Fe-Co-Ni series, which was confirmed experimentally. The best TE performance in this work was observed for the Cu2NiHf3S8 thiospinel due to its highest power factor and low thermal conductivity. Moreover, all the discovered compounds possess very low lattice thermal conductivity κlat over the investigated temperature range. The κlat for Cu2CoHf3S8 has been found to be as low as 0.8 W m-1 K-1 at 298 K and 0.5 W m-1 K-1 at 673 K, which are significantly lower values compared to the other Cu-based thiospinels reported up to date. The strongly disturbed phonon transport of the investigated alloys mainly comes from the peculiar crystal structure where the large cubic unit cells contain many vacant octahedral voids. As it was evaluated from the Callaway approach and confirmed by the speed of sound measurements, such a crystal structure promotes the increase in lattice anharmonicity, which is the main reason for the low κlat. This work provides a guideline for the engineering of thermal transport in thiospinels and offers the discovered Cu2MHf3S8 (M-Mn, Fe, Co, and Ni) compounds, as new promising functional materials with low lattice thermal conductivity.
ABSTRACT
Introduction: Nowadays, during formation and development of medicine, the main sector of health care is the protection of maternity and childhood. According to the Ministry of Health of Ukraine, inflammatory diseases of the reproductive system make up 60-65% of all gynecological diseases, among them inflammation of the fallopian tubes and ovaries is 79,6%, which occurs predominantly at young age. The aim is to study the microscopic structure of the oviducts wall in different anatomical parts during the embryonic period of human ontogenesis. Material and Methods: Were studied uterine tubes of the 4-10 months' embryos. We used a light microscopy method and morphometry to describe the peculiarities of oviducts' infundibulum, isthmus and ampullary part in fetus from 81 mm to 375 mm PCL. Results: The histotopography of the oviducts tunics and its parts (infundibulum, ampullary part, isthmus and uterine part) in the fetal period of ontogenesis is described in the article. The thickness of the oviduct wall in the dynamics of the fetal period increases in the direction from the infundibulum to the uterine part of the tube. The main part of the thickness of the oviduct wall is presented by muscles. The thickness of the circumferential muscle layer predominates over the thickness of the longitudinal in 2.5-2.8 times. Mucosa is thicker the isthmus, thinnest in the ampullary part of the uterine tube. Conclusions: The thickness of the infants oviduct wall in the dynamics increases in the direction from its infundibulum to the uterine part. The main part of the thickness of the oviduct wall is the tunica muscularis. The thickness of the circular muscle layer predominates the thickness of the longitudinal 2.5-2.8 times. Mucosa is thicker in the isthmus, the thinnest in the ampullary part. It is expedient to study the histotopography of the oviduct in the neonatal period of human ontogenesis.
