Formation Of Cation Vacancies Research Articles

Quaternary Mixed Oxides of Non-Noble Metals with Enhanced Stability during the Oxygen Evolution Reaction.

Robust electrocatalysts required to drive the oxygen evolution reaction (OER) during water electrolysis are still a missing component toward the path for sustainable hydrogen production. Here a new family of OER active quaternary mixed-oxides based on X-Sn-Mo-Sb (X = Mn, Fe, Co, or Ni) is reported. These nonstoichiometric mixed oxides form a rutile-type crystal structure with a random atomic motif and diverse oxidation states, leading to the formation of cation vacancies and local disorder. The successful incorporation of all cations into a rutile structure was achieved using oxidizing agents that facilitates the formation of Sb5+ required to form the characteristic octahedral coordination in rutile. The mixed oxides exhibit enhanced stability in both acidic and alkaline environments under anodic potentials with no changes in their crystal structure after extensive electrochemical stress. The improved stability of these mixed oxides highlights their potential application as scaffolds to host and stabilize OER active metals.

Atomistic oxidation mechanism of Bi0.5Sb1.5Te3 (0001) surface

Surface oxidation can potentially influence transport properties of thermoelectric materials and service performance of thermoelectric devices. Here, the oxidation mechanism of the (0001) surface of a widely used p-type TE material, Bi0.5Sb1.5Te3 (BST), was investigated using spherical aberration corrected scanning transmission electron microscopy (STEM). Combining atomic resolution STEM and density function theory (DFT), it was revealed that oxidation occurs at room temperature in the dry air through O diffusion into the surface quintuple layer, facilitating formation of both cation and anion vacancies, weakening the Bi-Te and Sb-Te bonds, leading to oxidation product Sb2O3, amorphous Te, and Bi-rich Bi2Te3. Formation of a thin O-rich cation-deficient quintuple layer on the surface and the Bi-rich BST region can significantly reduce the interfacial reaction between BST and Ni electrode, as the reaction layer thickness is reduced by 75% after the surface oxidation. This work provides essential structural information on surface oxidation mechanism and its influence on properties and performance of TE materials and devices.

Unexpected concentration dependence of Ba2+ dominant substitution in addition to La3+ in cubic Nd3+-doped BaLaLiWO6 perovskites

There is a great need in material science to find and investigate new RE3+ ion-doped inorganic materials suitable for producing sintered ceramics of high transparency.Prospective candidates for transparent ceramics should crystalize in highly symmetric crystal systems, so BaLaLiWO6 characterized by a cubic structure (s.g. Fm3¯m) seems to be a good candidate for accomplishing this highly challenging task.A series of micro-crystalline samples activated by Nd3+ ion (0–20 mol%) was produced via the solid-state reaction. Nd3+ ion was chosen as a laser dopant and structural probe. For the first time, the BaLaLiWO6 crystal structure was solved from the single crystal.The originality of this research results from the unexpected substitution of divalent Ba2+ ions by trivalent Nd3+ ones till up to 7 mol% and above this value the replacement of probably both Ba2+ and La3+ ions. Exchange of Ba2+ by Nd3+ ions leads to the formation of cationic vacancies due to the charge compensation effect: 3Ba2+ → 2Nd3+ + □ (vacancy in La3+ cationic sublattice), well-manifested in unit cell expansion with consequences in the spectroscopic characteristics. XRD and SEM methods in combination with emission and absorption spectroscopic ones used at cryogenic temperature helped to determine the substantial properties of this perovskite which could find application in optics. Slightly different cationic positions substituted by the Nd3+ ion and its non-homogeneous arrangement in the Ba2+/La3+ site, detected by spectroscopy with selective excitation under laser at 77 K, is pointed out. The crystal disorder of the cation environment is revealed in broad absorption and emission bands even at low temperature.

Bi compensation and poling process to enhance piezoelectric properties of BiFeO3-BaTiO3 lead-free piezoceramics

BiFeO3-BaTiO3 (BF-BT) ceramics are an excellent choice for high-temperature lead-free piezoelectric ceramic due to their high Curie temperature and good piezoelectric properties, but the volatilization of Bi leads to the formation of A-site cationic vacancies and oxygen vacancies, culminating in heightened leakage currents and detrimental effects on piezoelectric properties. In this study, a chemical composition of 0.70Bi(1+x)Fe0·97Al0·03O3-0.30BaTiO3 ceramics, abbreviated as B1+xFA-BT, where 0 ≤ x ≤ 0.05, were synthesized, with special attention on the effects of Bi compensation and poling process on their insulation and piezoelectric properties. Due to the coexistence of R-PC phases and low leakage current, B1+xFA-BT ceramics exhibit excellent piezoelectric properties and high Curie temperature, among which the B1.02FA-BT ceramic boasts optimal overall properties: d33 = 196 pC N−1, TC = 480 °C, kp = 34%, θmax = 49.5° and Qm = 32, under optimal poling parameters Ep = 50 kV cm−1 and Tp = 100 °C. The poling process is directly linked to the reorientation of domains, the redistribution of positive/negative space charge and the aggregation or injection of holes, which is achieved by tuning the poling field and temperature in a ceramic with optimal integrated piezoelectric properties. The poling process of BF-BT ceramics is significantly influenced by their leakage characteristics, which can have a significant impact on their overall performance. Optimizing electrical poling conditions and minimizing leakage current is crucial to achieving favorable piezoelectric properties in BF-BT ceramics with R-PC coexisting structures.

Ce-4f as an electron-modulation reservoir weakening Fe-O bond to induce iron vacancies in CeFevNi hydroxide for enhancing oxygen evolution reaction

Designing novel rare-earth-transition metal composites is at the forefront of electrocatalyst research. However, the modulation of transition metal electronic structures by rare earths to induce vacancy defects and enhance electrochemical performance has rarely been reported. In this study, we systematically investigate the mechanism by which Ce-4f electron modulation weakens the Fe-O bond, thereby altering the electronic structure in CeFevNi hydroxide to improve oxygen evolution reaction (OER) performance. Theoretical calculations and experimental characterizations reveal that Ce-4f orbitals function as electron-modulation reservoirs, capable not only of retaining or donating electrons but also of influencing the material's electronic structure. Moreover, Ce-4f bands optimize the Fe lower Hubbard bands (LHB) and O-2p bands, leading to weakened Fe-O bonds and the formation of cationic vacancies. This change results in the upshift of the d-band center at the active sites, favoring the reaction energy barrier for oxygen intermediates in the OER process. The synthesized catalyst demonstrated an overpotential of 201 mV at 10 mA cm−2 and a lifetime exceeding 200 h at 100 mA cm−2 under alkaline conditions. This work offers a proof-of-concept for the application of the mechanism of rare earth-induced transition metal vacancy defects, providing a general guideline for the design and development of novel highly efficient catalysts.

Oxygen vacancy migration and impact on high voltage DC polarization in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3

AbstractElectrical polarization and defect transport are examined in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3, an attractive capacitor material for high power electronics. Oxygen vacancies are suggested to be the majority charge carrier at or below 250°C with a grain conduction hopping activation energy of 0.97 eV and 0.92 eV for thermally stimulated depolarization current (TSDC) and impedance spectroscopy measurements, respectively. At higher temperature, thermally generated electronic conduction with an activation energy of 1.6 eV is dominant. Significant oxygen vacancy concentration is indicated (up to ∼1%) due to cation vacancy formation (i.e., acceptor defects) from observed Bi (and likely Zn) volatility. Oxygen vacancy diffusivity is estimated to be 10−12.8 cm2/s at 250°C. Low diffusivity and high activation energies are indicative of significant defect interactions. Dipolar oxygen vacancy defects are also indicated, with an activation energy of 0.59 eV from TSDC measurements. The large oxygen vacancy content leads to a short lifetime during high voltage (30 kV/cm), high temperature (250°C) direct current (DC) electrical measurements.

Dual Alloying Enables High Thermoelectric Performance in AgSbTe2 by Manipulating Carrier Transport Behavior

AbstractAgSbTe2 exhibits superior thermoelectric performance in the mid‐temperature region, but its electrical properties are strongly affected by intrinsic defects and secondary phases. Distinctively, the high mobility electrons still play an important role as minority carriers in p‐type AgSbTe2 even below the bipolarization temperature and decrease the Seebeck coefficient. Here, the Al and Se dual alloying can effectively increase the hole concentration by reducing the cation vacancy formation energy and simultaneously reduce the electron concentration by suppressing the n‐type Ag2Te secondary phase are demonstrated, which results in the shift of carrier transport from two‐type to one‐type as confirmed by Hall measurement. Consequently, through adjusting the ratio of hole and electron conductivity, the average power factor of alloyed sample is enhanced by 70%. Combined with further reduced lattice thermal conductivity resulting from high‐density stacking faults and superstructures, a maximum zT of 1.90 and an average zT of 1.42 are obtained in the temperature range of 323 to 623 K in the (AgSbTe2)0.98(AgAlSe2)0.02 sample. Finally, based on the finite element analysis modeling results, both single‐leg and double‐leg thermoelectric devices are fabricated, which show high conversion efficiency of 11.2% and 5.2%, respectively.

Dopant Control of Solution-Processed CuI:S for Highly Conductive p-Type Transparent Electrode.

Copper iodide (CuI) has garnered considerable attention as a promising alternative to p-type transparent conducting oxides owing to its low cation vacancy formation energy, shallow acceptor level, and readily modifiable conductivity via doping. Although sulfur (S) doping through liquid iodination has exhibited high efficacy in enhancing the conductivity with record high figure of merit (FOM) of 630 00MΩ-1, solution-processed S-doped CuI (CuI:S) for low-cost large area fabrication has yet to be explored. Here, a highly conducting CuI:S thin-film for p-type transparent conducting electrode (TCE) is reported using low temperature solution-processing with thiourea derivatives. The optimization of thiourea dopant is determined through a comprehensive acid-base study, considering the effects of steric hindrance. The modification of active groups of thioureas facilitated a varying carrier concentration range of 9×1018-2.52×1020cm-3 and conductivities of 4.4-390.7Scm-1. Consequently, N-ethylthiourea-doped CuI:S exhibited a FOM value of 7 600MΩ-1, which is the highest value among solution-processed p-type TCEs to date. Moreover, the formulation of CuI:S solution for highly conductive p-type TCEs can be extended to CuI:S inks, facilitating high-throughput solution-processes such as inkjet printing and spray coating.

Cation vacancy-boosted BaZnB4O8:xEu3+ phosphors with high quantum yield and thermal stability for pc-WLEDs.

Achieving high luminescent quantum yield and thermal stability of phosphors simultaneously remains challenging, yet it is critical for facilitating high-power white light emitting diodes (WLEDs). Herein, we report the design and preparation of the layered structure BaZnB4O8:xEu3+ (0.10 ≤ x ≤ 0.60) red phosphors with high quantum yield (QY = 76.5%) and thermal stability (82.8%@150 °C) by the traditional solid-state reaction method. The results of XRD and Rietveld refinement show that the presence of Eu3+ ions at Ba2+ sites causes the formation of cation (Zn2+/Ba2+) vacancies in the lattice. The PL and PL decay results reveal that the quenching concentration of BZBO:xEu3+ phosphors is as high as 50%, and the lifetime remains unchanged with Eu3+ concentration due to the unique structure of the host and the cation vacancies generated by the heterovalent substitution. Furthermore, on a 395 nm near-UV chip, a pc-WLED device with exceptional optical performance (CCT = 4415 K, CRI = 92.1) was realized using the prepared BZBO:0.50Eu3+ as a red phosphor. Simple synthesis and excellent performance parameters suggest that the reported BaZnB4O8:xEu3+ phosphors have promising applications in high-power pc-WLEDs. At the same time, it also indicates that cationic vacancy engineering based on heterovalent ion substitution is a potential strategy for improving luminescence quantum yield and thermal quenching performance.

Important factors of the A-site deficient Mn perovskites design affecting the CO oxidation activity

A-site deficient La0.4Sr0.4MnxTi1−xO3 (LSMT, x = 0, 0.4, 0.6, 0.8) perovskites were investigated for their structural change and effect on CO oxidation activity. The XRD, XPS, TPR and O2-TPD analysis represent the change in Mn concentration, known as an active species in oxidation, affecting the crystal structure, oxidation state of the B-site cation (Mn), number of oxygen vacancies, and the reducibility of the catalysts. The shift in the main perovskite diffraction peak in XRD spectra of the perovskites with a change in Mn content represents the formation of cationic vacancies. At the lower temperature (<200 oC), CO oxidation efficiency of LSMT perovskite catalysts was found to be almost identical. This can be attributed to their similar perovskite structure and surface area. Compared to the higher temperature (>200 oC) CO oxidation activity, the LSMT catalyst with lower Mn content of 0.4 shows relatively better performance than the higher Mn content samples, which signifies the active role of the Mn oxidation state and lattice oxygen species of the perovskite catalysts. Moreover, the LSMT4446 catalyst shows stable activity for more than 12 h with an average CO conversion of 80 %. From these results, we found that the factors of the Mn oxidation state and the type of oxygen species are crucial when designing an Mn-based perovskite catalyst for catalytic applications.

Preparation, luminescence, and application of LiMeBO3 borates, Me = Mg, Ca, Sr, Ba, Zn, Cd. Review

The review summarises and analyses data on the preparation, structure, and spectral-luminescent properties of LiMeBO3-based borates, Me = bivalent metal. These polycrystalline borates are prepared traditionally by solid-phase reactions and self-propagating high-temperature synthesis and its modifications based on a combustion reaction. Frameworks of lithium borates with alkaline earth metals, zinc, and cadmium are formed from large metal polyhedra between which there are boron-oxygen triangles isolated from each other. Doping with rare-earth and heavy metal ions leads to the formation of solid solutions which normally have defective structures. Doped activator ions often become the main part of the luminescence centre in the phosphor. The luminescent properties of ions of rare-earth elements arise from the possibility of electronic transitions between states within the 4f-configuration. The paper discusses the most likely mechanisms of charge compensation during heterovalent substitution in LiMeBO3 borates (co-doping and formationof cation vacancies). It is shown that charge compensation during the combined introduction of ions of REEs and alkali metals into the structure has a positive effect on the emission yield. The review considers the results of thermoluminescent, upconversion, and photoluminescent properties and processes and phenomena that cause them. It also explains the mechanism of resonance energy transfer from the sensitiser to the activator using the example of Yb3+→Er3+. It discusses the possibility of using the considered borates as phosphors that emit green, blue, and red light in white LEDs and as effective materials for personnel neutron dosimetry and the dosimetry of weak ionising radiation

Nucleation and growth mechanisms of ferrite on Mg–Ti–oxide surfaces: First-principles investigation

Fine and dispersed Mg–Ti–oxide inclusions, which act as heterogeneous nucleation sites for intragranular ferrite, have been acknowledged as an effective method for grain refinement. In this paper, the nucleation and growth mechanisms of ferrite on Mg–Ti-oxides surface were investigated through first-principles calculations and solid-state pressure bonding experiments. The calculated results show that the formation of cation vacancies is the limiting step for Mn solute atom absorption by Mg–Ti-oxides. As determined by the lower covalency and ionicity of the Mg–O bond compared to the Ti–O bond in Mg–Ti-oxides, Mn atoms will be efficiently absorbed by occupying the Mg vacancies. The experimental results demonstrate that MgTiO3 with the maximum Mn-depleted zone (MDZ) width is the most effective for ferrite nucleation, which is consistent with the calculation results. As a representative, the Fe(110)/MgTiO3(001) interface with the lowest planar disregistry (3.16%) was selected to analyze growth behaviors. Due to charge accumulation and variation, Fe atoms are more likely to gather on the Mg–O terminal MgTiO3(001) surface and form [(Mg–O)–Fe]-1 interfaces. Its adhesion work and interface energy are 1.74 and 2.46 J/m2, respectively. The present study illustrates the nucleation and growth mechanisms of ferrite on Mg–Ti-oxides, providing theoretical support for the application of Mg–Ti-oxide inclusions in oxide metallurgy.

Effect of Nb2O5 additive on the sintering behavior and properties of calcium hexaluminate

The present work focused on the effect of Nb2O5 additive on the sintering behavior and properties of CA6, aiming to optimize the crystal structure of CA6 and achieve the improvement in densification and properties. The results indicated that the formation of cation vacancies caused by the substitution of Al3+ with Nb5+ greatly promoted the CA6 grain to grow along the direction perpendicular to basal plane (c-axes), resulting in an improvement in the sintering densification. A significant increase in the cold compressive strength was observed due to the Nb2O5 additives, especially for the samples whose porosity decreased with Nb2O5 addition. Low porosity and the formation of the Ca(NbO3)2 phase were responsible for improving the slag resistance of the samples with Nb2O5 additives. Therefore, the introduction of Nb2O5 is expected to prepare CA6 materials with improved sintering densification, mechanical properties and slag resistance, promoting its better application in the metallurgical field.

Contrasting thermoelectric properties in cubic SnSe-NaSbSe2 and SnSe-NaSbTe2: High performance achieved via increasing cation vacancies and charge densities

Cubic SnSe has been recognized as one of the most promising mid-temperature thermoelectric candidates. Herein, the cubic-phase SnSe has been stabilized at room temperature by alloying NaSbSe2 and NaSbTe2, respectively, and the contrasting thermoelectric properties of SnSe-NaSbSe2 and SnSe-NaSbTe2 were systematically investigated. NaSbTe2-alloyed SnSe demonstrates better performance with especially higher electrical properties. According to the DFT calculations, the introduction of NaSbTe2 can bring the lattice parameter of cubic-phase SnSe closer to SnTe, leading to a lower cation vacancy formation energy and producing an ultra-high hole carrier concentration. Meanwhile, Te has a more developed charge density compared with that of Se, providing additional channels for charge transport when bonded to Sn atoms in cubic lattice. Limited by the electrical transport properties, the ZTmax for SnSe-NaSbSe2 only reaches ∼ 0.50 at 773 K, while the ZTmax for SnSe-NaSbTe2 approaches ∼ 0.95. Furthermore, sodium doping was utilized to tune the carrier mobility and carrier concentration of SnSe-NaSbTe2. Resultantly, the PFmax and ZTmax values reach ∼ 11 μW cm−1 K−2 and ∼ 1.20 at 773 K in sodium-doped SnSe-NaSbTe2, 4.4 and 3.0 times higher than those of pure SnSe, respectively. Our study further promotes cubic-phase SnSe thermoelectrics for mid-temperature energy harvesting applications.

High performance of Mg3Bi1.5Sb0.5 based materials for power generation: Revealing the counter-intuitive effect of tuning Bi content on the thermoelectric properties

Recently, Mg3Sb2-xBix alloys have attracted intensive attention, with the aim of maximizing the electrical transport performance via donor element doping, increasing the grain size, as well as electronic band structure engineering. However, less attention has been paid to other significant factors, like how these intrinsic point defects and accompanied secondary phases influence thermoelectric properties. In this study, the microstructure and thermoelectric transport properties of Mg3.2Sb0.5Bi1.495-xTe0.005 (x = 0 ∼ 0.2) compounds were systematically investigated, where tuning the Bi content shows the counter-intuitive impact on the thermoelectric properties. It was found that the Bi-poor environment associated with Bi impurities facilitated the increment of cation vacancy formation energy and then increased the carrier concentration, leading to the enhancement of power factor. Simultaneously, the reduction of Bi-rich second phase content weakened the carrier scattering by grain boundaries whereas high carrier mobility was maintained. Moreover, the bipolar thermal conductivity decreased obviously due to the increased majority carrier concentration to suppress the intrinsic excitation. The synergistic optimization pushes the average ZT value (300–573 K) up to 0.95 in the Mg3.2Sb0.5Bi1.295Te0.005 sample. Moreover, the calculated single-leg conversion efficiency is increased up to 9.7% with the hot-side temperature of 573 K, as the record-high value in this system.

Densification and Proton Conductivity of La1-xBaxScO3-δ Electrolyte Membranes.

Bain La1-xBaxScO3-δ impairs sintering and leads to a decrease in its ceramic density. Two approaches have been studied for obtaining dense ceramics: using a high processing temperature and the introduction of a Co3O4 sintering additive. An addition of only 0.5 wt% of Co3O4 sintering additive, despite the positive sintering effect, causes a noticeable violation of stoichiometry, with partial decomposition of the material. This can lead to the formation of cationic vacancies, which form associates with oxygen vacancies and significantly reduce the oxygen ion and proton conductivity of the materials. There is also a partial substitution of Co for Sc in La1-xBaxScO3-δ, which reduces the stability of protons: it reduces the enthalpy of the hydration reaction, but increases the mobility of protons. Thus, the Co3O4 sintering additive causes a complex of negative effects on the conductivity of La1-xBaxScO3-δ materials. Only high-temperature (1800 °C) processing with protection against Ba loss contributes to the production of dense La1-xBaxScO3-δ ceramics. The chemical composition of such ceramics corresponds well to the specified one, which ensures high water uptake and, consequently, high proton conductivity.

A first-principles investigation of point defect structure and energetics in ThO2

The structure and energetics of charged point defects in thorium dioxide (ThO2) have been investigated using the density functional theory (DFT) and phonon simulations. DFT simulations were performed under both zero-pressure and constant volume conditions. Termed as the free volume change of the point defects, the change in volume of the supercell has been computed in the zero-pressure case. Supercell expansion was observed with the increase of the (nominal) charge state of anion (O) interstitials and cation (Th) vacancies from neutral to its maximum. On the contrary, contraction of the supercell has been observed with anion vacancies and cation interstitials as the defect charge increases. The supercell volume change with respect to the charge state has been correlated with the resulting defect energetics. It has been observed that, as the defect charge increased, the internal energy and entropy of defect formation of the cation vacancies and anion interstitials were found to increase, while that of the cation interstitials and anion vacancies decreased. The temperature dependence of internal energy and entropy has also been examined. It was found that, as the temperature increases, the internal energies of the formation of cation vacancies and anion interstitials decrease, while those of the cation interstitials and anion vacancies increase. An opposite observation is seen for the entropies of formation defects when above room temperatures.

Y2Te3: A New n-Type Thermoelectric Material.

Rare-earth chalcogenides Re3-xCh4 (Re = La, Pr, Nd, Ch = S, Se, and Te) have been extensively studied as high-temperature thermoelectric (TE) materials owing to their low lattice thermal conductivity (κL) and tunable electron carrier concentration via cation vacancies. In this work, we introduce Y2Te3, a rare-earth chalcogenide with a rocksalt-like vacancy-ordered structure, as a promising n-type TE material. We computationally evaluate the transport properties, optimized TE performance, and doping characteristics of Y2Te3. Combined with a low κL, multiple low-lying conduction band valleys yield a high n-type TE quality factor. We find that a maximum figure of merit zT > 1 can be achieved when Y2Te3 is optimally doped to an electron concentration of 1-2 × 1020 cm-3. We use defect calculations to show that Y2Te3 is n-type dopable under Y-rich growth conditions, which suppress the formation of acceptor-like cation vacancies. Furthermore, we propose that optimal n-type doping can be achieved with halogens (Cl, Br, and I), with I being the most effective dopant. Our computational results as well as experimental results reported elsewhere motivate further optimization of Y2Te3 as an n-type TE material.

Dynamic active sites on plasma engraved Ni hydroxide for enhanced electro-catalytic urea oxidation

The urea oxidization reaction (UOR) is an important anodic reaction in electro-catalytic energy conversion. However, the sluggish reaction kinetics and complex catalyst transformation in electrocatalysis require activity improvement and better mechanistic understanding of the state-of-the-art Ni(OH)2 catalyst. Herein, by utilizing low-temperature argon (Ar) plasma processing, tooth-wheel Ni(OH)2 nanosheets self-supported on Ni foam (Ni(OH)2-Ar) are demonstrated to have improved UOR activity compared to conventional Ni(OH)2. The theoretical assessment confirms that the edge has a smaller cation vacancy formation energy than the basal plane, consequently explaining the structural formation. Operando and quasi-operando methods are employed to investigate the dynamic evolution of the Ni(OH)2 film in UOR. The crucial dehydrogenation products of Ni(OH)5O- intermediates are identified to be stable on the etched edge and explain the enhanced UOR in the low potential region. In addition, the dynamic active sites are monitored to elucidate the reaction mechanism in different potential ranges.

High Thermoelectric Performance of CaMg2Bi2 Enabled by Dynamic Doping and Orbital Alignment

AbstractSubstantial progress in improving the thermoelectric performance of CaMg2Bi2‐based materials has been made, yet existing reports barely discuss the effect of intrinsic Bi impurity on the transport properties. In this study, the first‐principles calculation shows that the Bi‐rich environment associated with Bi impurities facilitates the reduction of cation vacancy formation energy and then increases the carrier concentration. In addition, in the samples containing Bi impurity, a dynamic doping behavior caused by the redissolving of Bi second phase into the matrix with increasing temperature is identified experimentally, which force the carrier concentration to approach the optimal carrier concentration nH,opt, leading to a more than a 5 times enhancement of the figure‐of‐merit (ZT) compared to the single‐phase CaMg2Bi1.94. Moreover, by doping Ba and Yb on the Ca Site, orbital alignment is realized and phonon scattering is also enhanced. The synergistical optimization of electrical and thermal transportation brings a peak ZT of 1.24 at 873 K and a record ZTave of 0.86 (300–873 K) in (Ca0.5Yb0.25Ba0.25)0.995Na0.005Mg2Bi1.98 sample.