Real-world effectiveness and safety of vedolizumab induction therapy for ulcerative colitis: A prospective nationwide Polish observational study.

BACKGROUND: Vedolizumab is recommended as a first-line biological treatment, along with other biological drugs, in ulcerative colitis (UC) patients in whom conventional therapy failed and as a second-line biological treatment following a failure of a tumor necrosis factor alpha (TNF-α) antagonist. OBJECTIVES: We aimed to assess the real-world effectiveness and safety of vedolizumab induction therapy in UC patients treated in the scope of the National Drug Program (NDP) in Poland. MATERIAL AND METHODS: The endpoints were the proportions of patients who reached clinical response, clinical remission and mucosal healing at week 14. Partial Mayo scores, Mayo subscores and C-reactive protein (CRP) levels were also evaluated. RESULTS: Our study population consisted of 100 patients (55 biologic-naïve and 45 biologic-exposed). The median total Mayo score at baseline was 10 (interquartile range (IQR): 9-11), and 52 patients (52%) had extensive colitis. The clinical response at week 14 was achieved in 83 (83%) and clinical remission in 24 (24%) cases. Mucosal healing was observed in 56 (62%) patients at week 14. In patients with prior failure of biologic treatment (n = 25), 17 (68%) responded to vedolizumab treatment. A decrease in the median CRP level (from 3.7 mg/L to 2.6 mg/L) and the median total Mayo score (from 10 to 4) was observed. No new safety concerns were recorded and no patients discontinued the treatment due to adverse events (AEs). CONCLUSIONS: Vedolizumab was effective and safe as induction therapy for UC in a Polish real-world population including patients with severely active UC and a low number of patients with prior biological treatment failures.

Achieving high thermoelectric conversion efficiency in Bi2Te3-based stepwise legs through bandgap tuning and chemical potential engineering.

In this study, we show that the energy conversion efficiency in thermoelectric (TE) devices can be effectively improved through simultaneous optimization of carrier concentration, bandgap tuning, and fabrication of stepwise legs. n- and p-type Bi2Te3-based materials were selected as examples for testing the proposed approach. At first, the Boltzmann transport theory was employed to predict the optimal temperature-dependent carrier concentration for high thermoelectric performance over a broad temperature range. Then, the synthesized n-Bi2Te3-xSex and p-Bi2-xSbxTe3 solid solutions were tested to evaluate their suitability for fabricating the stepwise thermoelectric legs. The output energy characteristics of the designed TE devices were estimated using numerical modeling employing the finite element method. The theoretical simulation revealed an improvement in the conversion efficiency between the best homogeneous and stepwise TE legs from 8.8% to 10.1% and from 9.9% to 10.8% in p-type and n-type legs, respectively, which is much higher than the efficiency of the industrial thermoelectric modules (3-6%). The measured conversion efficiency of the fabricated n- and p-type stepwise legs reached very high values of 9.3% and 9.0%, respectively, at the relatively small temperature gradient of 375 K. This work suggests carrier concentration and bandgap engineering accompanied by the stepwise leg approach as powerful methods for achieving high energy conversion efficiency in thermoelectric converters.

Hardening of fcc hard-sphere crystals by introducing nanochannels: Auxetic aspects.

Tailoring the materials for a given task by modifying their elastic properties is attractive to material scientists. However, recent studies of purely geometrical atomic models with structural modifications showed that designing a particular change to achieve the desired elastic properties is complex. This work concerns the impact of nanochannel inclusions in fcc hard sphere crystal on its elastic properties, especially auxetic ones. The models containing six nanochannel arrays of spheres of another diameter, oriented along the [110]-direction and its symmetric equivalents, have been studied by Monte Carlo simulations in the isothermal-isobaric (NpT) ensemble using the Parinello-Rahman approach. The inclusions have been designed such that they do not affect the cubic symmetry of the crystal. The elastic properties of three different models containing inclusions of various sizes are investigated under four thermodynamic conditions. We find that six nanochannels filled with hard spheres of larger diameter increase system stiffness compared with the fcc crystal without nanoinclusions. The current finding contrasts the recently reported results [J.W. Narojczyk et al. Phys. Status Solidi B 259, 2200464 (2022)0370-197210.1002/pssb.202200464], where the fcc hard sphere crystal with four nanochannels shows reduced stiffness compared to the system without nanoinclusions. Moreover, the six nanochannel models preserve auxetic properties in contrast to the fcc hard sphere crystal with four nanochannel arrays, which loses auxeticity.

Structure Evolution and Bonding Inhomogeneity toward High Thermoelectric Performance in Cu2CoSnS4-xSex Materials.

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.

Real-world outcomes of 54-week vedolizumab therapy and response durability after treatment discontinuation in ulcerative colitis: results from a multicenter prospective POLONEZ study.

Background: Vedolizumab is a gut-selective anti-lymphocyte trafficking agent used to treat ulcerative colitis (UC) and Crohn's disease. Objectives: We aimed to evaluate the effectiveness, safety, and durability of the therapeutic effect of vedolizumab after treatment discontinuation in a real-world cohort of patients with UC treated in Poland. Design: This was a multicenter, prospective study involving patients with moderate to severely active UC from 12 centers in Poland who qualified for reimbursed treatment with vedolizumab between February and November 2019. Methods: The primary endpoints were clinical response (⩾2-point improvement from baseline on partial Mayo score) and clinical remission (partial Mayo score 0-1), including steroid-free remission, at week 54. Other outcomes included response durability at 26 weeks after treatment discontinuation, identification of predictors of response and remission, and safety assessment. Results: In all, 100 patients with UC were enrolled (55 biologic naïve and 45 biologic exposed). At baseline, 68% of patients were on corticosteroids and 45% on immunomodulators. Clinical response was observed in 62% of patients, clinical remission in 50%, and steroid-free remission in 42.6% at week 54. Within 26 weeks after treatment discontinuation, 37% of patients who maintained response by week 54 relapsed. The decreased number of liquid stools and rectal bleeding and endoscopic response at week 14 were predictive factors for response at week 54. Time from diagnosis ranging 2-5 years, decreased stool frequency, and non-concomitant use of corticosteroids at baseline and at week 14 were predictive factors for remission at week 54. Partial Mayo score < 3 with no subscale score > 1 at week 54 was a predictive factor for durable response after treatment discontinuation. The rate of serious adverse events related to treatment was 3.63 per 100 patient-years. Conclusion: Vedolizumab is effective and safe in UC treatment in Polish patients. However, the relapse rate after the treatment cessation was high. Registration: ENCePP (EUPAS34119).

Synergistic Effect of Work Function and Acoustic Impedance Mismatch for Improved Thermoelectric Performance in GeTe-WC Composite.

The preparation of composite materials is a promising methodology for concurrent optimization of electrical and thermal transport properties for improved thermoelectric (TE) performance. This study demonstrates how the acoustic impedance mismatch (AIM) and the work function of components decouple the TE parameters to achieve enhanced TE performance of the (1-z)Ge0.87Mn0.05Sb0.08Te-(z)WC composite. The simultaneous increase in the electrical conductivity (σ) and Seebeck coefficient (α) with WC (tungsten carbide) volume fraction (z) results in an enhanced power factor (α2σ) in the composite. The rise in σ is attributed to the creation of favorable current paths through the WC phase located between grains of Ge0.87Mn0.05Sb0.08Te, which leads to increased carrier mobility in the composite. Detailed analysis of the obtained electrical properties was performed via Kelvin probe force microscopy (work function measurement) and atomic force microscopy techniques (spatial current distribution map and current-voltage (I-V) characteristics), which are further supported by density functional theory (DFT) calculations. Furthermore, the difference in elastic properties (i.e., sound velocity) between Ge0.87Mn0.05Sb0.08Te and WC results in a high AIM, and hence, a large interface thermal resistance (Rint) between the phases is achieved. The correlation between Rint and the Kapitza radius depicts a reduced phonon thermal conductivity (κph) of the composite, which is explained using the Bruggeman asymmetrical model. Moreover, the decrease in κph is further validated by phonon dispersion calculations that indicate the decrease in phonon group velocity in the composite. The simultaneous effect of enhanced α2σ and reduced κph results in a maximum figure of merit (zT) of 1.93 at 773 K for (1-z)Ge0.87Mn0.05Sb0.08Te-(z)WC composite for z = 0.010. It results in an average thermoelectric figure of merit (zTav) of 1.02 for a temperature difference (ΔT) of 473 K. This study shows promise to achieve higher zTav across a wide range of composite materials.

Lone-Pair-Like Interaction and Bonding Inhomogeneity Induce Ultralow Lattice Thermal Conductivity in Filled ß-Manganese-Type Phases.

Finding a way to interlink heat transport with the crystal structure and order/disorder phenomena is crucial for designing materials with ultralow lattice thermal conductivity. Here, we revisit the crystal structure and explore the thermoelectric properties of several compounds from the family of the filled ß-Mn-type phases M 2/n n+Ga6Te10 (M = Pb, Sn, Ca, Na, Na + Ag). The strongly disturbed thermal transport observed in the investigated materials originates from a three-dimensional Te-Ga network with lone-pair-like interactions, which results in large variations of the Ga-Te and M-Te interatomic distances and substantial anharmonic effects. In the particular case of NaAgGa6Te10, the additional presence of different cations leads to bonding inhomogeneity and strong structural disorder, resulting in a dramatically low lattice thermal conductivity (∼0.25 Wm-1 K-1 at 298 K), being the lowest among the reported ß-Mn-type phases. This study offers a way to develop materials with ultralow lattice thermal conductivity by considering bonding inhomogeneity and lone-pair-like interactions.

Ultralow Lattice Thermal Conductivity and Improved Thermoelectric Performance in Cl-Doped Bi2Te3-xSex Alloys.

Bi2Te3-based alloys are the main materials for the construction of low- and medium-temperature thermoelectric modules. In this work, the microstructure and thermoelectric properties of Cl-doped Bi2Te3-xSex alloys were systematically investigated considering the high anisotropy inherent in these materials. The prepared samples have a highly oriented microstructure morphology, which results in very different thermal transport properties in two pressing directions. To accurately separate the lattice, electronic, and bipolar components of the thermal conductivity over the entire temperature range, we employed a two-band Kane model to the Cl-doped Bi2Te3-xSex alloys. It was established that Cl atoms act as electron donors, which tune the carrier concentration and effectively suppress the minority carrier transport in Bi2Te3-xSex alloys. The estimated value of the lattice thermal conductivity was found to be as low as 0.15 Wm-1 K-1 for Bi2Te3-x-ySexCly with x = 0.6 and y = 0.015 at 673 K in parallel to the pressing direction, which is among the lowest values reported for crystalline materials. The large reduction of the lattice thermal conductivity in both pressing directions for the investigated Bi2Te3-xSex alloys is connected with the different polarities of the Bi-(Te/Se)1 and Bi-(Te/Se)2 bonds, while the lone-pair (Te/Se) interactions are mainly responsible for the extremely low lattice thermal conductivity in the parallel direction. As a result of the enhanced power factor, suppressed bipolar conduction, and ultralow lattice thermal conductivity, a maximum ZT of 1.0 at 473 K has been received in the Bi2Te2.385Se0.6Cl0.015 sample.

Mechanism of Bonding Reactive Dyes with Copolymer (chloromethyl)oxirane-1H-imidazole cationised Cellulose.

Introducing the cellulose chain cationic groups in the modification process completely changes the charge on the cotton surface from negative to partially or totally positive. That allows the electrostatic attraction and simultaneous exhaustion and fixation of reactive dyes. This reaction can be carried out without salt and alkali at room temperature. Similarly, the reaction between reactive dye and an alone copolymer ([IME]+Cl-) with TLC chromatography was confirmed. The analysis with the use of particle optimisation with MM+ molecular mechanics and quantum-chemical calculations PM3 by the method of all valence orbitals confirmed the experimental results of the high activity of the nucleophile formed on the hydroxyl group in the chain of a modifier. It was found and experimentally confirmed that the reactive dyes during the dyeing process of the cotton cationised with copolymer (chloromethyl)oxirane -1H-imidazole ([IME]+Cl-) create covalent bonds due to a reaction with the hydroxyl group located in the modification agent instead of with the hydroxyl group in the glucopiranose ring. Although the dyeing takes place in very mild conditions, a high degree of setting is achieved, comparable to conventional methods.

Crystal Structure and Thermoelectric Properties of Novel Quaternary Cu2MHf3S8 (M-Mn, Fe, Co, and Ni) Thiospinels with Low Thermal Conductivity.

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.

Phase Analysis and Thermoelectric Properties of Cu-Rich Tetrahedrite Prepared by Solvothermal Synthesis.

Because of the large Seebeck coefficient, low thermal conductivity, and earth-abundant nature of components, tetrahedrites are promising thermoelectric materials. DFT calculations reveal that the additional copper atoms in Cu-rich Cu14Sb4S13 tetrahedrite can effectively engineer the chemical potential towards high thermoelectric performance. Here, the Cu-rich tetrahedrite phase was prepared using a novel approach, which is based on the solvothermal method and piperazine serving both as solvent and reagent. As only pure elements were used for the synthesis, the offered method allows us to avoid the typically observed inorganic salt contaminations in products. Prepared in such a way, Cu14Sb4S13 tetrahedrite materials possess a very high Seebeck coefficient (above 400 µVK-1) and low thermal conductivity (below 0.3 Wm-1K-1), yielding to an excellent dimensionless thermoelectric figure of merit ZT ≈ 0.65 at 723 K. The further enhancement of the thermoelectric performance is expected after attuning the carrier concentration to the optimal value for achieving the highest possible power factor in this system.

Removing Auxetic Properties in f.c.c. Hard Sphere Crystals by Orthogonal Nanochannels with Hard Spheres of Another Diameter.

Negative Poisson's ratio materials (called auxetics) reshape our centuries-long understanding of the elastic properties of materials. Their vast set of potential applications drives us to search for auxetic properties in real systems and to create new materials with those properties. One of the ways to achieve the latter is to modify the elastic properties of existing materials. Studying the impact of inclusions in a crystalline lattice on macroscopic elastic properties is one of such possibilities. This article presents computer studies of elastic properties of f.c.c. hard sphere crystals with structural modifications. The studies were performed with numerical methods, using Monte Carlo simulations. Inclusions take the form of periodic arrays of nanochannels filled by hard spheres of another diameter. The resulting system is made up of two types of particles that differ in size. Two different layouts of mutually orthogonal nanochannels are considered. It is shown that with careful choice of inclusions, not only can one impact elastic properties by eliminating auxetic properties while maintaining the effective cubic symmetry, but also one can control the anisotropy of the cubic system.

Extremely Non-Auxetic Behavior of a Typical Auxetic Microstructure Due to Its Material Properties.

The re-entrant honeycomb microstructure is one of the most famous, typical examples of an auxetic structure. The re-entrant geometries also include other members as, among others, the star re-entrant geometries with various symmetries. In this paper, we focus on one of them, having a 6-fold symmetry axis. The investigated systems consist of binary hard discs (two-dimensional particles with two slightly different sizes, interacting through infinitely repulsive pairwise potential), from which different structures, based on the mentioned geometry, were formed. To study the elastic properties of the systems, computer simulations using the Monte Carlo method in isobaric-isothermal ensemble with varying shape of the periodic box were performed. The results show that all the considered systems are isotropic and not auxetic-their Poisson's ratio is positive in each case. Moreover, Poisson's ratios of the majority of examined structures tend to +1 with increasing pressure, which is the upper limit for two-dimensional isotropic media, thus they can be recognized as the ideal non-auxetics in appropriate thermodynamic conditions. The results obtained contradict the common belief that the unique properties of metamaterials result solely from their microstructure and indicate that the material itself can be crucial.

High Thermoelectric Performance of p-Type PbTe Enabled by the Synergy of Resonance Scattering and Lattice Softening.

In this work, we show the simultaneous enhancement of electrical transport and reduction of phonon propagation in p-type PbTe codoped with Tl and Na. The effective use of advanced electronic structure engineering improves the thermoelectric power factor S2σ over the temperature range from 300 to 825 K. A rise in the Seebeck coefficient S was obtained due to the enhanced effective mass m*, coming from the Tl resonance state in PbTe. Due to the presence of additional carriers brought by Na codoping, electrical conductivity became significantly improved. Furthermore, Tl and Na impurities induced crystal lattice softening, remarkably reducing lattice thermal conductivity, which was confirmed by a measured low speed of sound vm and high internal strain CεXRD. Eventually, the combination of both the attuned electronic structure and the lattice softening effects led to a very high ZT value of up to ∼2.1 for the Pb1-x-yTlxNayTe samples. The estimated energy conversion efficiency shows the extraordinary value of 15.4% (Tc = 300 K, Th = 825 K), due to the significantly improved average thermoelectric figure of merit ZTave = 1.05. This work demonstrates that the combination of impurity resonance scattering and crystal lattice softening can be a breakthrough concept for advancing thermoelectrics.

Characteristics of patients with moderate-to-severe ulcerative colitis treated with vedolizumab: results from a Polish multicenter, prospective, observational real-life study (the POLONEZ study).

BACKGROUND: Vedolizumab, a humanized antibody targeting the α4ß7 integrin, was proven to be effective in the treatment of moderate-to-severe ulcerative colitis (UC) in randomized clinical trials. The aim of the POLONEZ study is to determine the demographic and clinical characteristics of the patients with UC treated with vedolizumab within the scope of the National Drug Program in Poland and to assess the real-world effectiveness and safety of vedolizumab in the study population. Here we report the demographic and clinical characteristics of these patients. METHODS: This prospective study included adult patients eligible for UC treatment with vedolizumab who were recruited from 12 centers in Poland between February and November 2019. Collected data included sex, age, disease duration, presence of extraintestinal manifestations or comorbidities, status of previous biologic treatment, and current concomitant treatment. Disease extent was determined according to the Montreal classification, and disease activity was measured with the Mayo Score. RESULTS: A total of 100 (55 biologic-naïve and 45 biologic-exposed) patients were enrolled in the study (51% female, median age 35 years). Among biologic-exposed patients (mostly infliximab-treated), 57% had failed to respond to the therapy. The disease duration was significantly shorter in biologic-naïve (median 5 years) than in biologic-exposed (8 years, p = 0.004) or biofailure patients (7 years, p = 0.04). In the overall population the median Total Mayo Score was 10. Disease extent and activity were similar between the subgroups. CONCLUSIONS: Our study indicates that patients treated with vedolizumab in Poland receive the drug relatively early after UC diagnosis, but their disease is advanced. More than half of the patients had not been treated with biologic drugs before initiating vedolizumab. The study was registered in ENCePP database (EUPAS34119). LAY SUMMARY: Characteristics of patients treated for ulcerative colitis with vedolizumab in Poland Treatment of moderate-to-severe ulcerative colitis (UC) with the integrin antagonist vedolizumab became available within the Polish National Drug Program (NDP) in 2018. In this study, for the first time, we provide detailed demographic and clinical characteristics of 100 patients (median age 35 years, 51% female) treated with vedolizumab in Poland, of whom 55 were biologic-naïve and 45 biologic-exposed. The median duration of disease was 6 years. The disease duration was shorter in biologic-naïve than in biologic-exposed patients. Most patients were affected by extensive colitis (52%) or left-sided colitis (42%). Median disease activity was 10 according to the Total Mayo Score. Sixty-eight patients received concomitant systemic corticosteroids and 45 patients received immunomodulators. Our findings indicate that Polish patients receiving vedolizumab have a high disease activity and are treated relatively early after UC diagnosis. This might be due to the criteria for inclusion of a patient in the NDP.

Entropy-Induced Multivalley Band Structures Improve Thermoelectric Performance in p-Cu7P(SxSe1-x)6 Argyrodites.

Searching for novel low-cost and eco-friendly materials for energy conversion is a good way to provide widespread utilization of thermoelectric technologies. Herein, we report the thermal behavior, phase equilibria data, and thermoelectric properties for the promising argyrodite-based Cu7P(SxSe1-x)6 thermoelectrics. Alloying of Cu7PSe6 with Cu7PS6 provides a continuous solid solution over the whole compositional range, as shown in the proposed phase diagram for the Cu7PS6-Cu7PSe6 system. As a member of liquid-like materials, the investigated Cu7P(SxSe1-x)6 solid solutions possess a dramatically low lattice thermal conductivity, as low as ∼0.2-0.3 W m-1 K-1, over the entire temperature range. Engineering the configurational entropy of the material by introducing more elements stabilizes the thermoelectrically beneficial high-symmetry γ-phase and promotes the multivalley electronic structure of the valence band. As a result, a remarkable improvement of the Seebeck coefficient and a reduction of electrical resistivity were observed for the investigated alloys. The combined effect of the extremely low lattice thermal conductivity and enhanced power factor leads to the significant enhancement of the thermoelectric figure of merit ZT up to ∼0.75 at 673 K for the Cu7P(SxSe1-x)6 (x = 0.5) sample with the highest configurational entropy, which is around twice higher compared with the pure selenide and almost four times higher than sulfide. This work not only demonstrates the large potential of Cu7P(SxSe1-x)6 materials for energy conversion but also promotes sulfide argyrodites as earth-abundant and environmentally friendly materials for energy conversion.

Cancellation of Auxetic Properties in F.C.C. Hard Sphere Crystals by Hybrid Layer-Channel Nanoinclusions Filled by Hard Spheres of Another Diameter.

The elastic properties of f.c.c. hard sphere crystals with periodic arrays of nanoinclusions filled by hard spheres of another diameter are the subject of this paper. It has been shown that a simple modification of the model structure is sufficient to cause very significant changes in its elastic properties. The use of inclusions in the form of joined (mutually orthogonal) layers and channels showed that the resulting tetragonal system exhibited a complete lack of auxetic properties when the inclusion spheres reached sufficiently large diameter. Moreover, it was very surprising that this hybrid inclusion, which can completely eliminate auxeticity, was composed of components that, alone, in these conditions, enhanced the auxeticity either slightly (layer) or strongly (channel). The study was performed with computer simulations using the Monte Carlo method in the isothermal-isobaric (NpT) ensemble with a variable box shape.

Origins of low lattice thermal conductivity of Pb1-xSnxTe alloys for thermoelectric applications.

Lead telluride is a well-established material for direct conversion of heat into electricity. However, the aspects of the heat transport phenomena for PbTe-alloys remain not fully understood. Here, for the first time, origins of the phonon scattering in Pb1-xSnxTe compounds were studied through changes in the effective anharmonic pair potential obtained from X-ray Absorption Fine Structure (XAFS) spectroscopy. Results indicate that the interatomic pair potential of Pb-Te and Sn-Te bonds changes with the level of substitution x and that the anharmonicity of bonds in the solid solution is increased leading to the lower values of the lattice thermal conductivity. Furthermore, due to the existence of a soft TO mode in Pb1-xSnxTe, the Grüneisen parameter γE determined using XAFS much more precisely corresponds with the changes of lattice thermal conductivity κlat compared to γS obtained from the speed of sound measurements. This study explains the observed drastic reduction in κL in Pb1-xSnxTe solid solution (2.3 W m-1 K-1 for PbTe vs. 1.0 W m-1 K-1 for Pb0.75Sn0.25Te), due to changes in the interatomic pair potential of Pb-Te and Sn-Te and provides guidelines into its effective modification related to thermal transport in alloys based on PbTe. The estimated range of low thermal conductivity for the PbTe-SnTe solid solutions (<1 W m-1 K-1) reveals opportunities for further enhancement of energy conversion for this promising family of compounds. Moreover, this work provides a new concept for the estimation of the Grüneisen parameter through the EXAFS spectra analysis.

Phase Equilibria and Thermoelectric Properties in the Pb-Ga-Te System in the Vicinity of the PbGa6Te10 Phase.

PbGa6Te10 is a promising thermoelectric (TE) material due to its ultralow thermal conductivity and moderated values of the Seebeck coefficient. However, the reproducible synthesis of the PbGa6Te10-based materials for the investigation and tailoring of physical properties requires detailed knowledge of the phase diagram of the system. With this aim, a combined thermal, structural, and microstructural study of the Pb-Ga-Te ternary system near the PbGa6Te10 composition is presented here, in which polycrystalline samples with the compositions (PbTe)1-x(Ga2Te3)x (0.67 ≤ x ≤ 0.87) and PbyGa6Te10 (0.85 ≤ y ≤ 1.5) were synthesized and characterized. Differential scanning calorimetry measurements revealed that PbGa6Te10 melts incongruently at 1007 ± 2 K and has a polymorphic phase transition at 658-693 K depending on composition. Powder X-ray diffraction of annealed samples confirmed that below 658 K, the trigonal modification of PbGa6Te10 exists (space groups P3121 or P3221) and above 693 K, the rhombohedral one (space group R32). A homogeneity range was found for PbyGa6Te10, y = 0.9-1.1, based on refined lattice parameters of PbyGa6Te10 in samples annealed at 873 K. The revised version of the PbTe-Ga2Te3 phase diagram in the vicinity of the PbGa6Te10 phase is proposed. Based on the new results of the phase equilibria, the TE properties of the PbyGa6Te10 samples were studied in detail. The deviation from the stoichiometric composition leads to a tuning of the charge transport in PbyGa6Te10, and as a result, the Seebeck coefficient and electrical conductivity were significantly modified over the homogeneity range. The Pb-deficient Pb0.9Ga6Te10 sample shows an improved power factor up to 9.5 µW m-1 K-2 and a reduced thermal conductivity as low as 0.17 W m-1 K-1 due to attuned chemical potential and additional scattering of phonons on point defects. Thus, the ZT parameter for this composition was improved up to ∼0.043 at 773 K, which is almost 4 times higher than that of the stoichiometric specimen. This work shows that the knowledge of phase equilibria and crystal chemistry plays a key role in improving the energy conversion efficiency for new functional TE materials.

Thermal conductivity of PbTe-CoSb3 bulk polycrystalline composite: role of microstructure and interface thermal resistance.

Systematic experimental and theoretical research on the role of microstructure and interface thermal resistance on the thermal conductivity of the PbTe-CoSb3 bulk polycrystalline composite is presented. In particular, the correlation between the particle size of the dispersed phase and interface thermal resistance (Rint) on the phonon thermal conductivity (κph) is discussed. With this aim, a series of PbTe-CoSb3 polycrystalline composite materials with different particle sizes of CoSb3 was prepared. The structural (XRD) and microstructural analysis (SEM/EDXS) confirmed the intended chemical and phase compositions. Acoustic impedance difference (ΔZ) was determined from measured sound velocities in PbTe and CoSb3 phases. It is shown that κph of the composite may be reduced when particle size of the dispersed phase (CoSb3) is smaller than the critical value of ∼230 nm. This relationship was concluded to be crucial for controlling the heat transport phenomena in composite thermoelectric materials. The selection of the components with different elastic properties (acoustic impedance) and particle size smaller than Kapitza radius leads to a new direction in the engineering of composite TE materials with designed thermal properties.