Bulk Thermal Expansion Coefficient Research Articles

Tailoring the coefficient of thermal expansion in a functionally graded material: Al alloyed with Ti-6Al-4V using additive manufacturing

Functionally graded materials enable the spatial tailoring of properties through controlling compositions and phases that appear as a function of position within a component. The present study investigates the ability to reduce the coefficient of thermal expansion (CTE) of an aluminum alloy, Al 2219, through additions of Ti-6Al-4V. Thermodynamic simulations were used for phase predictions, and homogenization methods were used for CTE predictions of the bulk CTE of samples spanning compositions between 100 wt% Al 2219 and 70 wt% Al 2219 (balance Ti-6Al-4V) in 10 wt% increments. The samples were fabricated using directed energy deposition (DED) additive manufacturing (AM). Al2Cu and fcc phases were experimentally identified in all samples, and aluminides were shown to form in the samples containing Ti-6Al-4V. Thermomechanical analysis was used to measure the CTE of the samples, which agreed with the predicted CTE values from homogenization methods. The present study demonstrates the ability to tailor the CTEs of samples through compositional modification, thermodynamic calculations, and homogenization methods for property predictions.

Structural, mechanical and thermodynamic stability of the CaIn intermetallic compound for promising hydrogen storage: ab-initio calculations

This study was conducted to investigate the structural, elastic, dynamical, mechanical, and thermodynamic properties of the binary intermetallic compound CaIn in various crystallographic phases, utilizing density functional theory (DFT) calculations. The results reveal that the compound is chemically and mechanically stable, as indicated by the formation energy, stability in the phonon dispersion, and elastic constants calculation. The mechanical and thermodynamic properties of our studied compound are only examined in the most stable calculated phase, which is the orthorhombic phase (Pmma). By calculating Pugh’s ratio it has been determined that this compound possesses a brittle character. The quasi-harmonic Debye (QHD) model was employed to analyze various thermodynamic parameters such as Debye temperature, volume variation, isothermal bulk modulus, heat capacity, and thermal expansion coefficient. These findings are expected to encourage further theoretical and experimental studies on the CaIn intermetallic compound for potential applications as a hydrogen storage material and in various other fields.

Low-cost thermal/environmental barrier coatings: A first-principles study

Development of low-cost advanced thermal/environmental barrier coating (T/EBC) materials with acceptable thermal and mechanical properties is essential for safeguarding ceramic composites substrate against thermal and chemical degradation, thereby enhancing the efficiency of components in the high-temperature section of gas turbine engines. To this end, we employed density functional theory-based approaches to predict the thermodynamic, mechanical, and thermal properties of rare earth disilicates based on abundant rare earth elements, namely La2Si2O7 and Ce2Si2O7, as potential alternatives to the current-state-of-the-art ytterbium disilicate EBCs that uses expensive and scarce element Yb. The present study predicts that G-phase Ce2Si2O7 has an ultralow thermal conductivity (0.26 W/m/K at 1500 K) and the apparent bulk coefficient of thermal expansion (ABCTE) (≈6.9 × 10-6 K−1) slightly higher than SiC, demonstrating great potential as low-cost high-performance T/EBC. However, La2Si2O7 and Ce2Si2O7 undergo an A- to G-phase polymorphic transition at around 1470 K, resulting in significant changes to crystal structure and lattice parameters, and accordingly CTE and lattice thermal conductivity.

First-principles calculations to investigate mechanical and thermodynamics properties of multi-anion oxycarbonitride ceramics TiCNO and TiZrCNO

Multicomponent ceramics have attracted increasingly attention due to their potential applications. Employing density functional theory (DFT) and the special quasi-random structure (SQS), the structural stability and elastic characteristics of TiCNO and TiZrCNO are systematically explored in this study. The available experimental data and the optimized lattice parameters coincide very well. Both high entropy oxycarbonitrides are thermodynamically stable because the formation enthalpies are negative. According to the present results of elastic parameters, the slight expense of the strength and stiffness the ductility is improved. The increase of ductility presumably originates from the multicomponent mixing in the anion sublattice, the subsequent incorporation of Zr results in the stronger influence due to the more severe lattice distortion, as discussed in our previous study. The anisotropy of two ceramics are studied systematically, the role of the anisotropy is explored in wear/cutting applications. Then the thermodynamic properties of the two ceramics are also studied further applying Debye-Grüneisen model. Thermodynamic properties of two materials exhibit essentially similar trends as temperature rises. Because the larger lattice distortion by the subsequent addition of Zr, the bulk moduli and thermal expansion coefficient for TiZrCNO change slowly with temperature. Clearly the influences of the multianion mixing, especially the contribution from the following incorporation of Zr which leads to larger internal distortion should pay high attention. The current investigations provide valuable insight into the mechanical and thermodynamic behavior of these two multicomponent ceramics.

Size-dependent heat capacity in nano-oxide crystals

Recent developments suggest that heat capacity of nano-oxides is size-dependent, since the product of bulk modulus (B) and thermal expansion coefficient (α) scales directly with isometric heat capacity Cv. Dependence of heat capacity on crystal-size Cv(d) is explored by examining Bαao where ao is the lattice parameter. Here Bαao(d)'s show maxima at 33 nm for ceria and at 14 nm for MgO and decrease with decreasing crystal-size (d) implying similar size-dependence for Cv if the Grüneisen parameter is size insensitive. Hence, the Cv (d) contradicts with metal's heat capacities which are larger in nano-grains. Contributions from grain boundaries and surfaces were posited for the difference. Besides phonons, free electrons in metals contribute to heat capacity. The absence of electronic carriers in oxides likely explains the difference.

First-principles study of crystal structure search, stability and mechanical property of magnesium-lithium binary system

In this paper, the energetically stable and metastable crystal structures of Mg-Li binary system are searched throughout all possible Mg concentrations by using the first-principles calculations based on density functional theory (DFT). Three stable structures are found at compositions LiMg, LiMg2 and Li2Mg3. One metastable structure is found at composition LiMg3. The formation energy, phonon spectrum, and elastic constants are calculated to evaluate the energy, dynamic and elastic stabilities, respectively. At zero temperature, both the elastic moduli (include bulk modulus B, shear modulus G, Young’s modulus E, the Poisson’s ratio ν and B/G ratio) as a function of the Mg concentration in Mg-Li binary system and the spatial direction dependences of elastic moduli are analyzed. The temperature dependents of bulk modulus and thermal expansion coefficient are also analyzed to investigate the high-temperature mechanical properties of Mg-Li binary system. With the increase of temperature, the bulk modulus of Mg-Li alloys gradually decreases and the thermal expansion coefficient gradually increases. And the calculated results also show that LiMg2 can maintain excellent mechanical strength and mechanical stability at high temperature, and has the potential of application in the high-temperature fields.

Proportional correlation between heat capacity and thermal expansion of atomic, molecular crystals and carbon nanostructures

Correlation between thermal expansions β(T) and heat capacity C(T) of atomic and molecular crystals, amorphous materials with a structural disorder, carbon nanomaterials (fullerite C60, bundles SWCNTs of single-walled carbon nanotubes) was analyzed. The influence of the contribution to the coefficient of linear thermal expansion αXe(T) of Xe atoms adsorbed on the SWCNTs bundles is considered. The proportional correlation was found between the contribution to the coefficient of linear thermal expansion αXe(T) and the normalized to the gas constant heat capacity C Xe(T)/R of Xe atoms adsorbed on the SWCNTs bundles. The proportional correlation (β/β*) ∼ (CV/R) with the parameter β* for the bulk thermal expansion coefficient for cryocrystals is proposed. In the case of atomic crystals such as Xe and Ar, the proportional correlation (β/β*) ∼ (CV/R) is observed in the temperature range from the lowest experimental to temperatures where CV/R ≈ 2.3. The correlation is not observed in the temperatures where 2.3 < C V/R < 3 (classical Dulong-Petit law). It was found that the universal proportional correlation is also observed for molecular crystals with linear symmetry, such as CO2, CO, and N2O if the normalized heat capacity below the values CV/R ≈ 3 ÷ 3.5. It indicates that the proportional correlation between thermal expansions (β/β*) and heat capacity (CV/R) is related not only to the translational, but also to the rotational degrees of freedom of the molecule in the crystal. In the case of the C0, molecular crystal with translational and rotational degrees of freedom and intramolecular vibrations, the discussed above correlation occurs below the values of normalized heat capacity CV/R ≈ 7.5. In strongly anisotropic systems, such as systems of compacted bundles of single-walled carbon nanotubes and SWCNTs bundles with adsorbed Xe atoms, this universal dependence appears in a limited temperature range that does not include the lowest temperatures. A qualitative explanation of the observed correlation is proposed.

Effect of the mesoporous size, structure and surface on the melting and heat transport properties of solar salt

Molecular dynamics simulations combined with experimental methods were used to summarize the changes of thermophysical parameters such as bulk thermal expansion coefficient, thermal conductivity, specific heat capacity at constant pressure and melting point, which based on the radial distribution function and interaction energy. The micro-mechanisms of the melting and heat transport properties of solar salts at the nanoscale were analyzed. The simulation and experimental results show that the bulk thermal expansion coefficient of solar salt decreases with the increase of the mesopore size. At the same scale, the bulk thermal expansion coefficient of the nanopillar solar salt is smaller than that of the spherical structure solar salt in the nanopore. The raising of the scale enhances the thermal conductivity of the solar salt, but has little effect on the specific heat capacity. The thermal conductivity and specific heat capacity of the CPCM are improved with the increase of Al 2 O 3 in the skeleton. The variation of the skeleton structure has a certain influence on the specific heat capacity of CPCM. The melting point of solar salt shows a trend of increasing and then decreasing with the raising of nanopore size. The change of the mesoporous structure affects the melting point of CPCM. The addition of the porous alumino silicate ceramic skeleton reduces the melting point of the solar salt. And the melting point of the CPCM with larger interfacial binding energy is relatively higher. • Correspondence between microscopic simulation and macroscopic thermal analysis data. • Micro analysis of scale effect on melting and heat transport proportions of CPCMs. • Micro analysis of structure effect on the melting and heat transport proportions of CPCMs. • Micro analysis of surface effect on the melting and heat transport proportions of CPCMs.

Structural Stability and Phase Transitions in Zeolite A: An In Situ High Pressure-High Temperature Investigation.

The high pressure-high temperature structural stability of Zeolite A (ZA) has been studied using the X-ray diffraction (XRD) method. Structural studies at high temperatures show a reduction in the oxygen occupancy, belonging to the water molecule, indicating thermal dehydration and subsequent expulsion of water molecules from the pores of the structure. ZA does not undergo structural phase transition with temperature. However, structural transitions are observed in in situ XRD studies at high pressure and high temperature. At 1.3 GPa and 300 °C, the cubic ZA concomitantly transformed to cubic sodalite (SOD) and tetragonal zeolite NaP (ZNP). This transition was completely forbidden at 2.7 GPa, where a temperature-induced amorphization was favored at 250 °C. The thermal studies at higher pressure reveal the marginal influence of pressure on the thermal expansion coefficients of hydrated ZA. Pressure evolution of the high pressure-high temperature phases indicates no further phase transitions up to 5.9 GPa. The equation of state fit to the pressure-volume data of these phases show that ZNP is less compressible, followed by SOD and ZA. In contrast to the behavior at 0.1 MPa, SOD shows a pressure-induced negative thermal expansion (NTE) at 5.9 GPa. On the other hand, the positive thermal expansion (PTE) observed along the direction of c axis is compensated by the NTE along the a axis leading to a negligible volume thermal expansion for the ZNP structure. The bulk moduli and thermal expansion coefficients of all of the observed phases are reported. The outcomes of this study have been consolidated as a pressure-temperature phase diagram, which provides an insight into the technological and industrial applications of ZA at extreme conditions.

Prediction of new stable phases of FePd2 crystal alloy

The stable crystal structures of FePd2 under ambient pressure are explored using the particle swarm optimization technique. In addition to the previously reported tetragonal I4/mmm, orthorhombic Immm and trigonal P3¯m1 phases, three as-yet-unreported phases with R3¯m, Cmcm, and P4/nmm space group are uncovered. Subsequent first principles calculations reveals that all phases have negative enthalpy of formation and the enthalpy of the tetragonal I4/mmm phase is the lowest. Also, these phases are mechanically and dynamically stable. Their ferromagnetism and metal ductility are confirmed by the electronic structure and Pugh's ratio. The bulk modulus of these phases are almost equal, and the I4/mmm structure has the relatively higher Young's modulus and shear modulus. The dimensionless magnetic hardness parameter demonstrated that the I4/mmm and P4/nmm structures are semihard magnets, and the other structures are permanent/hard magnetic materials, in which the Immm, Cmcm, and P3¯m1 structures are the potential candidates for ultra-high density magnetic storage. The results of the bulk modulus and thermal expansion coefficient at finite temperature show that the P3¯m1 structure as a promising high-temperature structural material.

Influence of mesoporous size and structure on heat transport characteristics of mixed nitrate

Molecular dynamics method is used to simulate the influence of the mesopore size and structure on the heat transport characteristics of the mixed nitrate. The Material Studio software is used to establish the mixed nitrate models of different scales and two structures, and the NaNO<sub>3</sub>-KNO<sub>3</sub> models of different proportions that reach the eutectic state. By calculating the models and sorting out the calculation results, the phase transition of mixed nitrates on a nanometer scale is calculated and the micro-mechanism of heat transport characteristics is analyzed. The results show that the phase transition temperature of the solar salt first increases and then decreases with the increase of the nanopore size, and finally is consistent with the melting point on a macro scale. The proportion of cations has a great influence on the phase transition temperature of mixed nitrate, and the nanowire structures also change the phase transition temperature of nitrate. The bulk thermal expansion coefficient of nitrate decreases with the increase of mesoporous size, increases with the increase of NaNO<sub>3</sub> content, and changes with the mesoporous structure. The enhancement of the interaction between ions will increase the thermal conductivity, but it will not have much effect on the specific heat capacity at a constant pressure.

A new guaninate hydrate K+·C5H4N5O−·H2O: crystal structure from 100 to 300 K in a comparison with 2Na+·C5H3N5O2−·7H2O

A new guanine salt hydrate, K+·C5H4N5O−·H2O, was obtained and characterized by single-crystal X-ray diffraction in the temperature range 100 K–300 K and compared with that of the previously documented sodium salt hydrate (2Na+·C5H3N5O2−·7H2O) [Gur & Shimon (2015). Acta Cryst. E71, 281–283; Gaydamaka et al. (2019). CrystEngComm, 21, 4484–4492]. Both sodium and potassium salt hydrates have channels. However, the structure of the channels, the cation coordination, the protonation (and, respectively, the charge) of the guanine anions, as well as the role of water molecules in the crystal structure are different for the two salt hydrates. In the crystal structures of the potassium salt, the guanine anions are linked via hydrogen bonds into quartets that form open cylindrical channels in a honeycomb framework. Water molecules `line the walls' of the channels, whereas the potassium cations fill the intra-channel space. This contrasts with the structure of the sodium salt hydrate in which guanine anions form channels with water molecules filling in the channel space together with sodium cations coordinating them. The 1D anionic assembly generated through numerous hydrogen bonds and cation interactions with guanine anions and water molecules is energetically the most distinctive part of the structure of the potassium salt hydrate. In the case of the guanine sodium salt, the structure contains purely inorganic polymeric fragments – sodium cations coordinated to a water molecule forming a 1D polymeric structure and guanine anions interconnecting these polymers via hydrogen bonds with water molecules. The structural differences account for the difference in the anisotropy of strain on temperature variation for the two salt hydrates: whereas in both structures the values of the bulk thermal expansion coefficients are similar in the two structures and the major expansion is observed along the channel axes, the degree of anisotropy for the K salt is more than four times higher than that for the Na salt.

Thermo Elastic Properties of Nano-TiO2 Under High Pressure Using Different Equations of State

In this paper, different EOSs (Birch-Murnaghan, modified Lennard-Jones, Singh and Kao, Tait) are used to study the effect of high pressure on thermo-elastic properties of nano TiO2 (Nano titanium dioxide). The results of V/Vo variation calculations under high pressure, using all the four EOSs, showed excellent agreement with the experimental data. This gives a conclusion that the EOSs used in the calculations of bulk materials, (Birch-Murnaghan, modified Lennard-Jones, Tait), can be used to perform the calculation for nanomaterials. The results obtained using these equations showed a complete agreement between them, on the one hand, and with the experimental data, on the other hand, when calculating the change of V/VO under high pressure. While the results obtained by S-K EOS differed from the results of the rest of the EOSs when calculating the change of, isothermal bulk modulus and thermal expansion coefficient, for Nano TiO2 under high pressure. This deviation may be attributed to considering B’O a constant value (B’O = 4) across all the derivation of S-K EOS.

Effect of pressure on mechanical and thermodynamic properties of Al<sub>7</sub>Cu<sub>2</sub>Fe phase

The band structures and elastic anisotropy of Al₇Cu₂Fe phase under various pressures are studied by using the Vienna ab-initio simulation package (VASP) based on density functional theory. The results show that Al₇Cu₂Fe phase is still metallic in the pressure range of 0 to 50 GPa and the pressure can improve the expansion of atomic orbital in the energy band. The elasti anisotropy in (100) and (010) planes of Al₇Cu₂Fe phase enhances with the increase of pressure, while the elasti anisotropy in (110) planes shows a fluctuating upward trend from 0 GPa to 50 GPa. Based on the quasi-harmonic Debye model, the changes of bulk modulus (B), Debye temperature (Θ_{<italic>D</italic>}), heat capacity (C_v and C_p) and thermal expansion coefficient (α) of Al₇Cu₂Fe phase with pressure and temperature are studied. The effects of applied pressure and temperature on thermodynamic properties of the Al₇Cu₂Fe phase is opposite. The values of B and Θ_{<italic>D</italic>} decrease with temperature and increase with the pressure. In addition, the variation trends of C_v, C_p and α under pressure and temperature are basically the same.

Molecular dynamics study of the point defects in bcc uranium

Thermodynamic properties of bcc uranium with point defects are studied using ab initio molecular dynamics (MD) simulations at 1100 K. The simulations were performed with canonical ensembles of ${\mathrm{U}}_{127}{\mathrm{M}}_{1}$, ${\mathrm{U}}_{128}{\mathrm{M}}_{1}$, and ${\mathrm{U}}_{126}{\mathrm{M}}_{1}{\ensuremath{\square}}_{1}$ for M = $\ensuremath{\square}$, He, Ne, Ar, Kr, Xe, Sr, Zr, I, Cs, and Pu disposed on a bcc lattice lying within a $4\ifmmode\times\else\texttimes\fi{}4\ifmmode\times\else\texttimes\fi{}4$ cubic supercell. This work provides formation energies of substitutional, self, and solute interstitial atom defects as well as binding energies of M-$\ensuremath{\square}$ pair defects. This work demonstrates that our computational scheme based on MD simulations gives reliable formation and binding energies of atomic defects in bcc uranium compared to conventional density functional theory calculations. The equilibrium volume, bulk modulus, and thermal expansion coefficient of pure bcc uranium obtained from our MD simulations compare very well with corresponding experimental results. The vacancy formation energy is predicted to be 0.88 eV. The experimental vacancy formation energy remains uncertain. Experimental study of the formation and binding energies of other point defects as well as the bulk modulus and thermal expansion coefficients of uranium with these defects is also not found in the literature. This work shows that point defects tend to decrease the bulk modulus and increase the thermal expansion coefficient of bcc uranium. The solute formation energies of noble gas atoms show a bearing on their size. A large solute (Xe) has a high formation energy, and vice versa. This size effect is not quite evident for the chemically reactive solutes, namely, Sr, Zr, I, Cs, and Pu. Our MD simulations further show that vacancies are the favorable point defects in bcc uranium rather than both vacancies and self interstitials as predicted by earlier calculations. The formation energies of self interstitial atoms are found to be lower than those of solute interstitial atoms, each calculated in six different basic interstitial dumbbell configurations. That is, bcc U accommodates self interstitials more easily than decay or fission gas interstitials (He, Kr, and Xe). Further, He atoms are found to have comparable formation energies in the substitutional and interstitial locations. The fission product atoms Kr and Xe prefer to occupy vacant substitutional lattice sites rather than interstitial sites. Binding energies of divacancy and solute-vacancy pairs (0.31 vs $\ensuremath{-}0.69$ eV for the Xe-$\ensuremath{\square}$ pair, for instance) from our MD simulation show that nucleation and growth of fission gas bubbles are supported by a thermodynamic driving force, whereas vacancies tend to stay apart. This is in agreement with literature reporting that bcc uranium softens and swells mainly by agglomeration of noble gas bubbles.

Insights into thermodynamic properties of CsCl-type HfTM (TM = Fe, Ru, Os) compounds from first-principles calculations

In this work, we used the first-principles calculations based on density functional theory and quasi-harmonic Debye to predict the electronic structures, phonon dispersions and thermodynamic properties of HfTM (TM = Fe, Ru, Os) compounds. The obtained phonon dispersions of HfTM indicate that they are thermodynamically stable. Moreover, HfFe, HfRu and HfOs show metallic properties from the electronic structures. The bulk moduli and thermal expansion coefficients of HfTM compounds under temperature of 0 ~ 1500 K and pressure of 0 ~ 20 GPa were considered, and the results indicate that the bulk modulus reduces as the temperature increases, and thermal expansion coefficient changes quickly to temperature at low temperatures. The order of thermal expansion coefficient is HfFe > HfRu > HfOs and that of thermal stability is HfOs > HfRu > HfFe. Besides, Debye temperature is opposite to the trend of Gruneisen parameter under the same temperature and pressure.

Thermal and compressional behavior of the natural borate kurnakovite, MgB3O3(OH)5·5H2O

The thermal and compressional behaviors of kurnakovite, a potential B-rich aggregate in neutron radiation-shielding concretes, were studied by in situ single-crystal synchrotron X-ray diffraction (100–393 K, 0–13.36(5) GPa). Above 393 K, the crystal structure collapses in response to dehydration. The bulk thermal expansion coefficient is αV(298K) = 5.18(1)∙10−5 K−1. Volume compressional trend modelled with a Birch-Murnaghan equation of state yields a bulk modulus of KP0,T0 = 35(3) GPa. A phase transition occurs between 9.23(5) and 11.11(5) GPa, leading to a triclinic high-P polymorph (with triple unit-cell volume) and to an increase in coordination of one third of the trigonal-planar boron sites to a tetrahedral geometry.

High performance and low thermal expansion in Er-Fe-V-Mo dual-phase alloys

Low thermal expansion alloy plays a unique role in high precision instruments and devices owing to its size stability under thermal shocks. However, a low thermal expansion generally produces a poor mechanical performance, such as brittleness and low fracture resistance, which is a bottle-neck for their applications as functional materials. Here, we demonstrate a novel intermetallic compound-based dual-phase alloy of Er-Fe-V-Mo with excellent structural and functional integrity achieved by precipitating a ductile phase in the hard-intermetallic matrix with large magnetovolume effect. It is found that the compound with 12.8 ± 0.1vol% precipitate phase improves the alloy's strength and toughness by one order of magnitude, while keeping a low bulk coefficient of thermal expansion (1.87±0.02 × 10−6K − 1) over a wide temperature range (100 to 493 K). The combined analyses of real-time in-situ neutron diffraction, synchrotron X-ray diffraction, and microscopy reveal that both the thermal expansion and the mechanical properties of the precipitate phase are coupled with the matrix phase via semi-coherent interfacial constraint; more importantly, the precipitate phase undergoes a pronounced strain hardening with dislocation slips, which relieves the stress localization and thus hinders the microcrack propagation in the intermetallic matrix. Moreover, the alloys are easy to fabricate and stable during thermal cycling with great application potentials. This study shed light on the development of low thermal expansion alloys as well as the implications to other high-performance intermetallic-compound-based material design.

Structural stability of Sc3CrO6: A Raman spectroscopic study

AbstractStructural stability of the mixed rare earth‐transition metal oxide Sc3CrO6 (space group ) is investigated at high pressures using Raman spectroscopy up to 23.8 GPa, at ambient temperature. Results indicate that the compound transforms reversibly to a lower symmetry phase above 18 GPa. Lattice dynamical calculations carried out using a shell model were used to obtain the bulk modulus and to estimate mode Grüneisen parameters from Raman spectroscopic data. From the nature of changes in the vibrational spectra and from the trends in iso‐structural compounds, we speculate the high pressure phase to be a monoclinic phase. On the other hand, temperature dependent Raman scattering studies in the temperature range 77–1,273 K, indicate disappearance of a few vibrational modes indicating increase in symmetry. From the pressure and temperature dependence of the Raman modes, using calculated bulk modulus and thermal expansion coefficient, anharmonicity of the modes is estimated. It is found that anharmonicity due to phonon–phonon decay is more dominant and the contribution of thermal expansion is small for all of the Raman modes.

Thermoelectric properties and thermal expansion of quaternary layered compound SrFZnSb

Abstract Layered semiconductors have received increased attention recently due to the potential as high-performance thermoelectric materials. The quaternary layered compound SrFZnSb adopts ZrSiCuAs-type structure with insulating [Sr2F2]2+ layers and conductive [Zn2Sb2]2+ layers alternately stacked along the c-axis. As a narrow band-gap p-type semiconductor, SrFZnSb has a higher electrical conductivity and smaller Seebeck coefficient in comparison with isostructural thermoelectric compound BiOCuSe. Thermal properties measurements for pristine SrFZnSb reveal that its total thermal conductivity drops to 1.33 W m−1 K−1 at 773 K with the lattice thermal conductivity fitting the law of T−1. The maximum thermoelectric figure of merit ZT for SrFZnSb reaches 0.17 at 773 K. In addition, SrFZnSb presents the bulk thermal expansion coefficient of 1.2–1.5 × 10−5 K−1 within the temperature range of 300–700 K, smaller than 6.74 × 10−5 K−1 for BiOCuSe.