Thermoelectric Behavior Research Articles

Effect of vacancies on structural, electronic, elastic, and thermoelectric properties of CdIn[formula omitted]Se[formula omitted] defect chalcopyrite-type semiconductor: An ab-initio approach

In this work, we have investigated the detailed structural, electronic, elastic, mechanical and thermoelectric properties of pure (CdInSe2) and defect (CdIn2Se4) chalcopyrite-type semiconductors using the ab-initio approach within the density functional theory along with semi-classical Boltzmann transport theory. The structural properties reveal the pure structure is more distorted than the defect one. The electronic band structure infers that the pure structure is an n-type semiconductor while the defect one is an intrinsic semiconductor having a larger bandgap as compared to the former due to the cationic vacancy. Both compounds are direct bandgap semiconductors. From the calculation of elastic stiffness constants and elastic moduli, it is found that both the compounds are mechanically stable. The melting temperature of CdInSe2 and CdIn2Se4 are obtained as 831 K and 784 K, respectively. The electronic thermoelectric properties show a higher value of ZT = 0.86 for the ordered vacancy compound (CdIn2Se4) with a fixed hole concentration of 1020 cm−3 at 800K making it competent for the thermoelectric applications. The variation of various thermoelectric coefficients w.r.t. the chemical potential shows that in CdIn2Se4, the p-type doping is favorable to further enhance the thermoelectric behavior. The lattice thermal conductivity for the defect structure is found to be 3.78 W/mK at room temperature and a lowest value of 1.421 W/mK at 800K. The results demonstrate the defect CdIn2Se4 as a promising thermoelectric material.

Effect of Shunt Resistor Value on the Performance of Resistive Superconducting Fault Current Limiters

Resistive-type superconducting fault current limiters (r-SFCLs) have generated great interest for research and technical applications. This is attributed to their superior features, which include self-action, fast response, and simple operation. In low line impedance systems, r-SFCLs are seen as a viable protective mechanism for limiting high-magnitude fault currents. However, overcurrent caused by faults results in an increased temperature of the r-SFCL, possibly damaging the coils. Thus, the r-SFCL must be appropriately engineered to protect it while still allowing for effective fault current limitation. To achieve this goal, an appropriately sized shunt resistor must be used. Adding a shunt resistor benefits the r-SFCL in several ways, from lowering its maximum temperature to speeding up its recovery. Additionally, the shunt resistor protects the r-SFCL from excessive surges in temperature by giving the current an alternative path to flow down, thus saving it from further damage. A multilayer thermoelectric model was developed to examine the thermoelectrical behavior of the r-SFCL coil throughout a fault occurrence and the subsequent recovery period using three shunt resistors ranging from 4 to 16 Ω. MATLAB®/Simulink was used as the simulation platform in this study. The dependence of the current limitation capability and the voltage profile on the shunt resistor value was studied compared to the basic case without an r-SFCL. Increasing the shunt resistor value led to an enhanced ability to limit fault currents, although at the cost of higher temperatures and a longer recovery time. This study also presents guidance for optimizing the design parameters of r-SFCLs.

Study of electronic, thermoelectric, and optical response of zinc oxynitride thin films

In this research work, we have used density functional theory (DFT) and experimental approaches to explore the impact of nitrogen substitution on the electronic, thermoelectric, optical and structural aspects of Zn Ox=1−y Ny compounds with varying dopant content. The ZnO band gap was shown to progressively decrease with the successive increases in N concentration in theoretical and experimental estimated results. The thermoelectric properties of pristine and N-doped ZnO compositions were analyzed by employing Boltztrap measurements. The structural, morphological, and optical properties of sputtered thin films were studied extensively. X-ray diffraction studies exhibited the monophasic hexagonal wurtzite structure without any secondary phase. Field emission scanning electron microscopy was performed to examine the surface morphologies of the prepared thin films, which depicted that the higher dopant content caused grain agglomeration. Optical parameters were extracted using spectroscopic ellipsometry measurements and the optical band gap was inferred using Tauc plot. Importantly, the sample having maximum dopant content revealed tunable ENZ response in the NIR region. It is anticipated from computed simulation and experimental outcomes that the electronic, optical, and thermoelectric behavior of ZnO compounds could be enhanced by ensuing nitrogen inclusion. These engineered materials would be well-suited for optoelectronic applications within the visible and near-infrared energy regions as well as in thermoelectric applications.

Bandgap tuning, mechanical and thermoelectric properties of Cs2CuScX6 (X = Cl, Br, I) halide ion substitution for optoelectronic devices using density functional theory

As a result of their exceptional optoelectronic properties, the growing need for renewable and sustainable energy has heightened interest in perovskites. Using DFT, mechanical, electronic, optical, and thermoelectric properties of double perovskites (DPs) Cs2CuScX6 (X = Cl, Br, I) were analyzed to gain a comprehensive understanding of these materials. To ensure structural and thermal stability, permissible values for the tolerance factor (tG) and energy of formation (ΔHf) have been determined. The bandgap values of Cl, Br, and I-based compositions are recorded as 1.9 eV, 1.80 eV, and 1.70 eV, respectively. According to their bandgap, Cs2CuScBr6 and Cs2CuScI6 DPs determine the suitability of the materials for use in ideal photovoltaic devices. Further, optical properties are investigated in the energy range 0–10 eV, indicating visible and ultraviolet absorption. The investigated compound Cs2CuScI6 exhibited the highest visible spectrum absorption, making it an ideal candidate for solar cell applications. Moreover, the BoltzTrap code have been used for thermoelectric behaviour for temperature shows that all double perovskites have high Seebeck coefficients and low thermal conductivities.

Thermoelectric behavior of Bi2Te2.55Se0.45 with a tunable seebeck coefficient: A comparison between coarse needle-like structure and bulk nanostructured alloys

In this study, we compare the thermoelectric properties of coarse-grained n-type Bi2Te2.55Se0.45 alloy prepared by induction melting with the bulk-nanostructured prepared by ball milling and hot-pressing techniques. The corresponding thermoelectric properties showed different behavior for each material processed using different routes. The most striking result of the study is observing a p-type behavior and charge carrier transition from p-to n-type for the coarse-grained alloy. These observed phenomena are related mainly to the unique needle-like microstructure accompanied by high lattice strain. Lastly, the obtained figure-of-merit values for the coarse needle-like structure and bulk nanostructured Bi2Te2.55Se0.45 alloys are 0.20 and 0.80 at their optimum temperatures of 60 and 120 °C, respectively.

Bipolar thermoelectrical SQUIPT (BTSQUIPT)

We theoretically study the quasiparticle current behavior of a thermally biased bipolar thermoelectrical superconducting quantum interference proximity transistor, formed by a normal metal wire embedded in a superconducting ring and tunnel-coupled to a superconducting probe. In this configuration, the superconducting gap of the wire can be modified through an applied magnetic flux. We analyze the thermoelectric response as a function of magnetic flux, at fixed temperatures, in the case of a device made of the same superconductor. We demonstrate magnetically controllable, bipolar thermoelectric behavior and discuss optimal working conditions by looking at the thermoelectric power and other figures of merit of the device.

Negative temperature coefficient and positive temperature coefficient behavior of electrically conductive silicone/carbon black composites

As highlighted in several studies, the thermal expansion of the polymer matrix plays an important role with respect to the thermo-electrical behavior of conductive composites. Although it is known that the crosslink density of polymers affects the thermal expansion of polymers, no studies are known on whether different crosslink densities can affect the thermoelectric behavior of electrically conductive composites. In this study, silicone/carbon black composites with different crosslink densities, were investigated with respect to their self-heating properties under applied voltages and their thermo-electrical behaviors like positive and negative temperature coefficients. Specific resistances ρ about 55 +/− 4.5 Ω-cm have been achieved and uniquely high negative temperature as well as low temperature coefficients were demonstrated, which make these materials interesting for sensor-technical applications. Regarding their self-heating behaviors, average surface temperatures of up to 147°C were measured, which further make these materials very interesting as flexible heating elements. Finally, it could be shown that the crosslink density of addition curing silicones is adjustable over a wide range and that it can be further significantly changed by the addition of carbon black and platinum content.

Carrier and morphologically tailored thermoelectric properties of MBi2O4 (M=Cu, Ni, and Zn) kusachiites

In this article, we first report the newly evolved MBi2O4 (M = Cu, Ni and Zn) kusachiite's thermoelectric properties in the mid-temperature range. The material's structure and surface morphology are tailored to influence the thermoelectric properties. CuBi2O4, NiBi2O4, and ZnBi2O4 kusachiite compounds were synthesized via an efficient solvothermal method. MBi2O4 shows variation in thermoelectric transport behavior with different transition metals at the ‘M’ site. CuBi2O4 and NiBi2O4 show p-type transport properties at 303 K. Whereas ZnBi2O4 shows n-type transport properties at 303 K and with rising temperature transitions from n-type to p-type due to stochiometric deviation of cations. MBi2O4 has increased electrical conductivity at the end of the examined temperature, where ions dominate the conduction. The presence of Cu+ and Ni3+ uplifts the electrical transport behavior of CuBi2O4 and NiBi2O4 than ZnBi2O4. The thermal conductivity of NiBi2O4 falls below 1 Wm−1K−1 in the entire measured temperature and that of ZnBi2O4 decreases with the increasing temperature. The porous surface of NiBi2O4 act as phonon scattering centers. Further, NiBi2O4 structure and porosity were found to be efficient for thermoelectric applications due to the influence of Ni.

Separation of electric and thermal transport with in-situ precipitates matrix in Ca3Co4O9+δ

Suppressing the thermal conductivity of materials through the reduction of the particle sizes has long been applied to enhance the thermoelectric performance of nanostructured materials. Maintaining a high electrical conductivity in the as-formed nanostructure that is comparable to its bulk materials, is equally important in determining the final thermoelectric behavior of the nanostructure. However, this is not always attainable since the phononic and electronic transport in solids is often interdependent on each other. Naturally occurring with a complex layered structure, bulk polycrystalline Ca3Co4O9+δ has been selected to investigate the subtle correlation between electronic and phononic subsystems, which is still challenging for complex thermoelectrics. By combining high-energy ball milling and spark plasma sintering (SPS), we generate a novel structure of CCO matrix with in-situ precipitates, in which the bar-shaped CCO grains form a three-dimensional network, and the Co3O4 polyhedrons are found to be attached to the CCO grain surfaces with CaCO3 nano-precipitates filling the network space. The CCO grains serve as electrical paths to maintain the high electrical conductivities, while the in-situ precipitates, especially CaCO3, have significantly blocked the phonon transport in the bulk CCO samples with nanocrystalline grains, thus greatly reducing the thermal conductivity. Electrochemical analysis and the modified Debye-Callaway calculation provide a substantial understanding for the transport of charge carriers and phonons. A record zT value of 0.5 with ultra-low thermal conductivity of 0.496 Wm−1K−1 at 973 K are achieved in the CCO-66 sample. To date, this is the highest reported zT value in undoped polycrystalline CCO material systems.

First-principles calculations to investigate structural, electronic, optical and thermoelectric properties of novel double perovskite Cs2CeAgX6 (X = Cl, Br) for optoelectronic and thermoelectric applications

The present study unveils physical characteristics, including elastic parameters, phonon dispersion, electronics, optical, and thermoelectrics behavior’s novel double perovskite Cs2CeAgX6(X = Cl, Br) by performing FP-LAPW computational approach. The mechanical stability of studied compounds has been addressed rigorously, and both compounds are ductile, revealing their potential for the fabrication of optoelectronic and thermal devices. Moreover, the phonon dispersion advocated about dynamical stability of the Cs2CeAgX6(X = Cl, Br) compounds. Both studied compounds have shown a wider band gap, a clear signature of a semiconductor nature. Spin-polarized electronicband structure's outcomes as well as electronic density of states have been computed using TB-mBJ approximation.Moreover, Cs2CeAgBr6 offers a reduced gap rather then Cs2CeAgCl6. The photo response analysis shows that Cs2CeAgBr6 can absorb various ultraviolet (UV) and visible electromagnetic radiations. Henceforth, Cs2CeAgBr6 is found to be a more suitable aspirant for optoelectronic device fabrication. Regarding composites' thermoelectric behaviour, the Seebeck coefficient reflects that studied materials are hole-based semiconductors computed by the BoltzTrap code. Cs2CeAgCl6 has shown a higher thermal conductivity magnitude than Cs2CeAgBr6, so It's a potential thermoelectric material devices and allied applications.

Comparative study between charge and spin thermoelectric figure of merits in an antiferromagnetic ring

Considering the unique and diverse characteristic features of antiferromagnetic (AFM) systems, here in our work, we explore spin-dependent thermoelectric behavior in an AFM ring geometry. A reasonably large ( ≫1 ) spin figure of merit, referred to as Z S T, is obtained under suitable input conditions. Two important prerequisites are (i) breaking the symmetry among up and down spin sub-Hamiltonians and (ii) generating different asymmetric transmission line shapes across a Fermi energy for two opposite spin electrons. Describing the physical system within a tight-binding framework, where spin-dependent scattering occurs due to the interaction of itinerant electrons with local magnetic moments via the usual spin-moment exchange interaction, we compute all the thermoelectric quantities based on Landauer integrals following the Green’s function technique. The behavior of charge figure of merit, denoted as Z C T, is also discussed along with Z S T. Though Z C T reaches above unity, it is much smaller compared to Z S T. This is the key finding of our investigation. To make the present communication a self-contained one, we compare the results with another arrangement of magnetic moments in a ring-like geometry and in a chain-like one. Our analysis gives a suitable hint that in the presence of spin-dependent scattering, much more favorable energy conversion can be substantiated.

Dynamical thermoelectric transport properties of graphene: MF approach

In the present work, Seebeck coefficient and Figure of merit in terms of thermoelectric, electric, and thermal scattering rates employing powerful technique of memory function formalism in graphene system are investigated. This study leads to the dynamical thermoelectric transport behavior of graphene subjected to electron–phonon interactions using linear response theory. Within premises, explicit expression of generalized Drude scattering rate or imaginary part of memory function associated with thermoelectric/electric/thermal functions is studied. In zero frequency (DC regime) and low-temperature limit, Seebeck coefficient shows the linear-T dependence and, is found to be good in agreement with the experimental and theoretical results. Further, several frequency and temperature dependent transport coefficient results for electron–phonon scattering in graphene are performed. We found that S(ω,T) shows saturation at ω≫ωBG and raises with temperature below the Bloch–Grüneisen (BG) frequency regime (ω≪ωBG). We numerically investigated thermoelectric Figure of merit (ZT) with frequency/temperature domains and discussed.

Simulation and comparative study of the effect of the electrical connection between the battery electrodes on the battery thermal behavior

Accurately simulating and characterizing the thermal behavior of lithium batteries is vital for thermal design and management. Currently, the widely used simulation method for studying battery module thermal behavior and management is the virtual electrical connection. However, this method overlooks the presence of the busbar. Therefore, this study utilizes a physical electrical connection simulation method to investigate the impact of busbar heat generation and transfer on the thermoelectric behavior of the battery module. The results indicate that the busbar's heat production and transfer significantly affect the current density and temperature distribution, as well as the temperature uniformity of the battery module. The physical electrical connection simulation method accurately models the actual current transfer process between the battery electrodes, aligning with the real-world operation. In comparison to the virtual electrical connection simulation method, the physical electrical connection approach shows elevated local temperatures at the battery electrodes and the upper area in proximity to the busbar. It also exhibits more significant temperature gradients and worse temperature uniformity. Under real-world driving conditions, the temperature and heat generation of the battery undergo more frequent and wider fluctuations compared with constant-current discharge. The impact of the busbar's heat production and transfer on battery thermal behavior becomes more evident in these conditions. For example, under the FTP75, NEDC, and WLTC conditions, the maximum temperature increased by 8.04 °C, 28.43 °C, and 27.35 °C respectively, and the maximum temperature difference increased by 7.91 °C, 28.41 °C, and 27.19 °C respectively. Thus, the physical electrical connection simulation method significantly enhances the realism of battery module thermoelectric behavior simulations, contributing to the accuracy and effectiveness of thermal management analysis and product design.

The narrow band bap double perovskites X2CuInCl6 (X = K, Rb, Cs) for optoelectronics, and thermoelectric applications

The lead free, non-toxic, dynamically stable behavior of double perovskites make them promising materials for thermoelectric and optoelectronic applications. Therefore, the mechanical, optoelectronic, and transport characteristics of X2CuInCl6 (X = K, Rb, Cs) are addressed comprehensively by density functional theory. The phonon dispersion band structures are computed for dynamic stability, and tolerance factor for structural stability. The band structures show narrow band gaps (0.25, 0.42, 0.56) eV which are significantly important for infrared detectors and other optoelectronic devices operating with visible and IR light. The absorption peaks of maximum intensity are noted at 1.5 eV (827 nm), 2.0 eV (620 nm), and 2.5 eV (496 nm) for K, Rb, and Cs based DPs. Furthermore, thermoelectric behavior has been analyzed by the figure of merit, power factor, Seebeck coefficient, electrical to thermal conductivity ratio against chemical potential (−0.1 eV to 0.1 eV) and temperature (100–500 K). The ultralow values of lattice vibration, and large ZT increase their importance for thermoelectric generators.

Investigation of thermoelectric response, mechanical stability and thermodynamic behavior of Sr2MgPdO6 and Sr2MgPtO6 double perovskites: A DFT insights

The Density Functional Theory (DFT) study of Sr2MgPdO6 and Sr2MgPtO6 double perovskite compounds has been carried out to explore the properties of these materials and their nature. It was observed that these compounds are formed into crystals of cubic perovskite structural arrangement which resides with the Fm-3m (No.225) space group. Electronic band structure confirmed that these double perovskite oxides are semiconductors in nature. The estimated elastic constants and other mechanical parameters confirmed the ductile nature of Sr2MgPdO6 and Sr2MgPtO6. The thermodynamic properties include entropy, internal energy, specific heat, and vibrational free energy are observed for these double perovskites. Using BoltzTrap software, the thermoelectric behavior of these materials has been investigated by calculating electrical conductivity and electronic thermal conductivity concerning scattering time, and Seebeck-coefficient. Power factor and figure of merit are also calculated with the help of these parameters to check the applicability of the materials for waste heat recovery systems and advanced technologies.

Direct observation of hot-electron-enhanced thermoelectric effects in silicon nanodevices

The study of thermoelectric behaviors in miniatured transistors is of fundamental importance for developing bottom-level thermal management. Recent experimental progress in nanothermetry has enabled studies of the microscopic temperature profiles of nanostructured metals, semiconductors, two-dimensional material, and molecular junctions. However, observations of thermoelectric (such as nonequilibrium Peltier and Thomson) effect in prevailing silicon (Si)—a critical step for on-chip refrigeration using Si itself—have not been addressed so far. Here, we carry out nanothermometric imaging of both electron temperature (Te) and lattice temperature (TL) of a Si nanoconstriction device and find obvious thermoelectric effect in the vicinity of the electron hotspots: When the electrical current passes through the nanoconstriction channel generating electron hotspots (with Te~1500 K being much higher than TL~320 K), prominent thermoelectric effect is directly visualized attributable to the extremely large electron temperature gradient (~1 K/nm). The quantitative measurement shows a distinctive third-power dependence of the observed thermoelectric on the electrical current, which is consistent with the theoretically predicted nonequilibrium thermoelectric effects. Our work suggests that the nonequilibrium hot carriers may be potentially utilized for enhancing the thermoelectric performance and therefore sheds new light on the nanoscale thermal management of post-Moore nanoelectronics.

Dehydrated polyvinyl alcohol as novel carbon material filler for poly (3,4-ethylenedioxythiophene): Poly (styrene sulfonate) based composites with enhanced thermoelectric behavior

Readily available carbon materials produced from polyvinyl alcohol (PVA) were used as fillers to prepare polymer-inorganic composite films with poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) as stabilizer. Polyacetylene-like aerogel structures with high carbon contents were obtained when PVA was pyrolyzed at 300 °C (PVA-300). PEDOT: PSS interact strongly with PVA-300 due to their conjugated chemistry which benefits π-π overlap. The structural and computational results have proved that a conformationally organized PEDOT: PSS interfacial layer templated by PVA-300 aerogel produces higher conductivity in PEDOT: PSS/PVA (PP) composite films than that in pure PEDOT: PSS. The charge transfer process also promotes carrier transport of the electrically conductive network of PP composites. These special characteristics lead to the optimal power factor of 259.56 μ W m−1 K−2 and ZT value of 0.49 at 300 K in PP composite with 25 wt% PVA-300. A flexible thermoelectric generator (TEG) with 14 thermoelectric p-type PP units is demonstrated, which gives an output voltage of 146 mV at ΔT = 70 °C.

Coupling of magnetism, crystal lattice, and transport in EuCuP and EuCuAs

EuCuP and EuCuAs are members of a family of materials with candidates for realizing magnetically tuned electronic topology. In this work, the magnetic phase transitions and magnetoelastic coupling of EuCuP and EuCuAs have been investigated. Around the Curie temperature, the thermal expansion coefficient and specific-heat capacity of EuCuP are found to have two closely spaced features, at approximately 30 and 31.3 K, which may indicate a cascading magnetic transition or perhaps an electronic transition closely coupled to the magnetic ordering. The zero-field magnetoelastic coupling appears to be stronger in EuCuP than in EuCuAs, and field-dependent measurements suggest this is due to the dominant ferromagnetic interaction in EuCuP as opposed to antiferromagnetic order in EuCuAs below ${T}_{\mathrm{N}}=13.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Thermal expansion is anisotropic around ${T}_{\mathrm{N}}$ in EuCuAs, with a maximum expansion along [001] occurring above ${T}_{\mathrm{N}}$ prior to a stiffening of this $c$-axis component on cooling through ${T}_{\mathrm{N}}$; the expansion of the basal plane has a lambda-like peak centered slightly above ${T}_{\mathrm{N}}$. Matching these behaviors, the ac susceptibility data for EuCuAs suggest the presence of strong ferromagnetic correlations above ${T}_{\mathrm{N}}$ in the vicinity where the $c$-axis expansion peaks. Both compounds possess similar electrical and thermoelectric transport behaviors, with short-range magnetic order likely playing an important role above ${T}_{\mathrm{C}}$ or ${T}_{\mathrm{N}}$. Transport properties suggest these are predominantly hole doped due to intrinsic defects, and narrow-gap semiconducting or semimetallic behavior may be achievable if the underlying defects can be tuned.

First-Principles Study on Lithium Intercalation in Traditional Semiconductors Leading to Investigation of Structural Stability and Thermoelectric Properties of Their 2D Structures

In this study, we systematically investigated the lithium intercalation into nearly 30 traditional wurtzite phase semiconducting group II–VI, III–V, and IV–IV compounds. As a result, the compounds formed different structural types of layers, i.e., monolayer, bilayer, ladder-type, ribbon-type, and unexfoliated type. In addition, we correlated the reaction’s progress using each of their bulk Pauling ionic radii. After that, 20 exfoliated layers of compounds were studied. As an outcome of these calculations, they can be classified into three distinct 2D layers, which are monolayer (ML), double layer honeycomb (DLHC), and double layer square lattice (DLSL). By using the first-principles calculations to study the structural, mechanical, dynamical, electronic, and thermoelectric properties of 20 2D layers in order to determine their distinctive characteristics, our results show that most of these 2D layers are dynamically and mechanically stable. Electronic properties show that ML and DLHS structures exhibit a semiconducting nature, while the DLSL structure shows a high conducting nature. Finally, the thermoelectric behavior reveals that 20 2D layers possess outstanding figures of merit (ZT) in the range of 0.5–1.0 at 300 K, thereby they can be used as thermoelectric applications.

The effects of Zn doping on the thermoelectric performance of Cu12Sb4S13

In this study, first-principles electronic structure calculations and Boltzmann transport theories were used to understand the thermoelectric behavior of tetrahedrites. Calculations were performed on zinc (Zn)-substituted derivatives with zinc occupying each lattice site in the parent compound Cu12Sb4S13 to study the zinc substitution mechanism and the relation between the zinc substitution site and thermoelectric performance. It was found that the most energetically favorable sites for zinc are the Cu(1) sites, and the next are the Cu(2) sites. Furthermore, the room-temperature Seebeck coefficient of the host was enhanced nearly 255 and seven times by zinc doping at Cu(1) and Cu(2) sites, respectively, owing to the decrease in carrier concentration and the increase in band effective mass, respectively. However, the electrical conductivity showed a marked decrease upon zinc doping at Cu(1) and Cu(2) sites, due to the decrease in carrier contribution and low mobility, respectively. As a result, Cu12Sb4S13 compounds substituted with zinc at Cu(1) sites have a preferable optimizing power factor at room temperature. The optimizing power factor of the host could obtain approximately eight times improvement at room temperature upon zinc substitution at Cu(1) sites.