The effect of phase transition of crednerite/delafossite CuMn1−xCrxO2 on optical,thermal, and power factor properties

This study aims to investigate the effect of the phase transition of CuMn_1−xCr_xO₂ compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn_1−xCr_xO₂ samples were synthesized by a solid-state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO₂ to delafossite CuCrO₂ was confirmed by X-ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X-ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed-state Mn³⁺/Mn⁴⁺ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn_1−xCr_xO₂. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO₂ phase to the delafossite CuCrO₂ phase on CuMn_1−xCr_xO₂ compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties.     

Effects of Fe doping on structure,negative thermal expansion,and magnetic properties of antiperovskite Mn3GaN compounds

We synthesized antiperovskite Mn₃Ga_1−xFe_xN (0 ≤ x ≤ 0.30) compounds and investigated their negative thermal expansion (NTE) behavior, structure, and magnetic properties. A high-resolution transmission electron microscopy analysis and a selected-area electron diffraction (SAED) pattern indicate that the samples have high crystallinity with a single-phase cubic structure. Tunable NTE behavior appears below room temperature, and the NTE operation temperature range (△T) is broadened while increasing the Fe doping. Furthermore, introducing Fe in Mn₃Ga_1−xFe_xN can efficiently adjust the NTE coefficient from −232.57 × 10⁻⁶/K (x = 0) to −12.57 × 10⁻⁶/K (x = 0.20), and the corresponding △T can be broadened from △T = 22 K to 51 K. Besides, the total entropy change (ΔS_total) at the phase transitions continuously decreases from 9.2 to 4.7 J/(kg K) while increasing the Fe content from x = 0.05 to 0.10. With increasing Fe into Ga sites, the magnetic ordering varies from antiferromagnetic (AFM) to ferromagnetic (FM), the AFM to paramagnetic (PM) phase transition temperature decreases, whereas the FM to PM transition temperature increases when increasing the Fe content. The present study indicates that magnetic element doping can efficiently tune the NTE and the correlated physical features of the antiperovskite compounds.     

Dielectric and electric relaxations induced by the complex defect clusters in (Yb+Nb) co‐doped rutile TiO2 ceramics

The effect of the Yb+Nb substitution for Ti on the microstructure, crystal structures, and dielectric properties of (Yb_1/2Nb_1/2)_xTi_1?xO₂ (0.01≤x≤0.1) ceramics is investigated in this study. The results reveal that the solid solubility limit of the (Yb_1/2Nb_1/2)_xTi_1?xO₂ ceramics is x=0.07, and the average grain sizes considerably decrease from 12 μm to 6 μm with x increasing from 0.01 to 0.1. Three types of dielectric relaxations are observed at temperature ranges of 10‐30 K, 80‐180 K, and 260‐300 K, caused by the electron‐pinned defect dipoles, polaron hopping, and interfacial polarizations, respectively. The conduction mechanism changes from nearest‐neighbor‐hopping to polaron hopping mechanism, which is confirmed by ac conductivity measurements. The present work indentifies the correlation between the colossal permittivity and polaron hopping process in the titled compound.     

Effect of texturing on thermal,electric and elastic properties of MoAlB,Fe2AlB2, and Mn2AlB2

Herein, MoAlB, Fe₂AlB₂, and Mn₂AlB₂ with textured microstructures were sinter-forged from pre-reacted preforms in a hot press at 1400, 1200, and 1050 °C, respectively. X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the textured nature and high phase purities. The effect of texturing on the thermoelectric properties was evaluated by measuring thermal diffusivities, electrical resistivities, and Seebeck coefficients on the sinter-forged samples and those of less textured, reactively hot-pressed samples. While the thermoelectric properties were essentially isotropic for sinter-forged Fe₂AlB₂ and Mn₂AlB₂, differences included electron-dominated thermal transport in Fe₂AlB₂ and phonon-dominated transport in Mn₂AlB₂ over most of the 323–873 K range. Magnetic phase transitions at 281 K in Fe₂AlB₂ and 308 K in Mn₂AlB₂ were identified in electrical resistivity measurements. MoAlB was found to have anisotropic thermoelectric properties, with notably small relative Seebeck coefficients ranging from ? 2 μV/K at 323 K and increasing to 5 μV/K at 873 K.     

Enhanced temperature coefficient of resistance and magnetoresistance of Co-doped La0.67Ca0.33MnO3 polycrystalline ceramics

Recently, La_0.67Ca_0.33MnO₃ has garnered significant research attention due to its peculiar physical properties, such as colossal magnetoresistance and metal insulator transitions. The practical applications of these materials are mainly determined by the temperature coefficient of resistance (TCR) and magnetoresistance (MR). As a mature synthesis route, the sol-gel method can prepare high-quality ceramic targets. Herein, using methanol as a solvent, La_0.67Ca_0.33Mn_1-xCo_xO₃ (0 ≤ x ≤ 0.06) polycrystalline ceramics are prepared using the sol-gel method and the influence of Co doping on electrical and magnetic properties is systematically studied. Co doping increases the grain size, and is helpful to improve TCR and MR. In addition, with increased Co doping, the double exchange is weakened, and the ferromagnetism is depressed, which leads to a decrease in T_MI. The results reveal that the TCR and MR can be optimized by tuning the Co content. For instance, we have achieved a TCR value of 44.2% · K^?1 at x = 0.02 and an MR value of 76.3% at x = 0.04, showing the promise of Co-doped La_0.67Ca_0.33MnO₃ ceramics in a wide array of applications, such as bolometers and magnetic sensors.     

Effect of Fe substitution on temperature coefficient of resistance and magnetoresistance of La0.67Ca0.33MnO3 polycrystalline ceramics

La_0.67Ca_0.33MnO₃ perovskite manganate exhibits high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, these enable novel multifunctionalities. Mn site substitution can change magnetic order of the manganates, thereby tailoring both electrical and magnetic transport. Herein, La_0.67Ca_0.33Mn_1-xFe_xO₃(0 ≤ x ≤ 0.06) polycrystalline ceramics were prepared by sol-gel route. The effect of Fe substitution on TCR and MR of La_0.67Ca_0.33MnO₃ was studied. Fe replacing Mn ions, would weaken double exchange, and significantly reduced Curie temperature and ferromagnetism. Additionally, Fe doping promoted the development of grain. TCR increased first with Fe content x and then decreased, and reached 45.2%·K^-1 at x = 0.01, which is the highest value reported. Notably, with Fe doping, MR gradually increased and reached 81.1% (1 T) at x = 0.06. Fe doping can significantly enhance TCR and MR, which generates promising potential in (uncooled) thermistor/infrared detecting and magnetic sensors.     

Highly enhanced thermoelectric performance in BiCuSeO ceramics realized by Pb doping and introducing Cu deficiencies

In recent years, BiCuSeO oxyselenides have been developed as a promising thermoelectric material. In this article, Pb_xBi_1−xCu_1−ySeO (x = y = 0, 0.02, 0.04, 0.06, and 0.08) are prepared by solid-state reaction method and spark plasma sintering (SPS), and the combinatorial effects of Pb doping and Cu deficiencies on thermoelectric properties are investigated systematically. The transport properties are significantly enhanced due to the optimized carrier density, majorly contributing to the promotion of ZT values. As a result, the maximum ZT of 0.77 at 873 K and average ZT (from 300 to 873 K) of 0.50 are obtained for Pb_0.06Bi_0.94Cu_0.94SeO sample. The values are 0.4 and 1.2 times, respectively, higher than that of pristine sample.     

High thermoelectric performance of (Bi1-xPrx)2(Te0.9Se0.1)3 alloys prepared by high-pressure sintering method

In this article, n-type (Bi_1-xPr_x)₂(Te_0.9Se_0.1)₃ (x = 0, .002, .004, .008) alloys were fabricated by high-pressure sintering (HPS) method together with annealing. The effect of high pressure and Pr contents on the microstructure and thermoelectric performance of samples were explored in detail. The results show that the HPS samples are composed of nanoparticles. Pr doping has significant impacts on the electrical and thermal transport properties of the Bi₂Te_2.7Se_0.3 alloys. The HPS sample with x = .004 shows the maximum ZT value of .31 at 473 K, which is enhanced by 41% to compare with the Pr-free sample. Annealing can improve the thermoelectric properties by increasing the electrical transport properties and decreasing the thermal conductivity simultaneously. As a result, the highest ZT value of 1.06 is achieved for the annealed sample with x = .004 at 373 K, which is beneficial to the thermoelectric power generation.     

Effect of manganese stoichiometry at B-site on magneto-transport and magnetic properties of La0.67Sr0.33MnO3manganites

To study the effect of manganese non-stoichiometry at B-site, a series of manganites with compositional formula La_0.67Sr_0.33Mn_1±xO₃ (where x = 0, 0.05 and 0.1) was synthesized by oxalate precursor method. X-ray diffraction data confirm the rhombohedral structure of La_0.67Sr_0.33Mn_1±xO₃ along with minor phases of Mn₃O₄. The average grain size is found to be 266 nm for x = 0 whereas its magnitude decreases with excess or deficiency in manganese concentration. An increase in the manganese non-stoichiometry leads to the coexistence of ferromagnetic and antiferromagnetic interactions. The effect of Mn_1±x on the magnetotransport properties could be understood on the basis of collective behaviour of magnetic spins, double exchange mechanism and ratio of Mn⁴⁺/Mn³⁺ ions. A crossover from negative to positive magnetoresistance behavior above metal-insulator transition temperature was observed for LSP-0.95 sample, whereas a positive magnetoresistance over the entire temperature region was noticed for LSP-1.10 sample.     

Development and characterization of (1-x)BiYO3-xBiMnO3 ceramics for Ferro-photovoltaic applications

The rare combination of ferroelectricity, low band gap and high carrier mobility in a material can facilitate exceptional photovoltaic efficiency. In this paper, we attempted to reduce the band gap and improve the conductivity of ferroelectric solid solution BiY_(1-x)Mn_xO₃ by varying composition. The BiY_(1-x)Mn_xO₃ (x = 0.0, 0.10, 0.25, 0.50, 0.75) samples were prepared by high energy ball milling method and structural, dielectric, optical, electrical and ferroelectric properties were analyzed systematically. Herein, we show that band gap of the material is drastically reduced from 3.0 eV (BiYO₃) to 1.76 eV (x = 0.50) and the samples exhibit ferroelectric behavior with significant polarization. Compound resistance of grain and grain boundaries were also found to reduce with increase in Mn concentration in the BiY_(1-x)Mn_xO₃ solid solution, demonstrating improvement in semiconducting behaviour of the material. Thus, solid solution formation of BiMnO₃ with BiYO₃, tunes band gap in useful region, improves electrical conduction and enhances ferroelectric polarization showing good potential for high performance solar cell and thermoelectric applications.     

Enhanced microwave absorption properties of Y-Co2Z/PANI hexaferrites composites in the frequency range of 0.1–18 GHz

We prepared Ba_3−xY_xCo₂Fe₂₄O₄₁ (Y-Co₂Z, x = 0, 0.2, and 0.4) by the solid-state reaction method. Y-Co₂Z and polyaniline (PANI) composites (named as Y-P0, Y-P2, and Y-P4) were prepared by using the in-situ polymerization method. The Y-doping played an important role in the variation of lattice parameters, a and c. The combination of Y-doping and PANI modified the magnetic properties of the composites, which could be observed by the changing of the saturation magnetization and coercivity. This combination had also affected the electromagnetic properties of composites through the measurements of complex permittivity and permeability. Using the transmission line theory, we calculated refection loss (RL) of composites with the variation thickness of 1.00–2.50 mm. Our composites tuned the minimum RL from the X band (RL = −29.6 dB at 11.4 GHz for Y-P2) to Ku band (RL = −16.3 dB at 15.7 GHz for Y-P4 and RL = −26.4 dB at 16.6 GHz for Y-P4). For maximum effective bandwidth, our composites covered a huge range from the S and C bands (Y-P0 with 3.9 GHz in the range of 3.4–7.3 GHz) through the X band (Y-P2 with 3.9 GHz in the range of 9.0–12.9 GHz) to the Ku band (Y-P4 with 4.0 GHz in the range of 13.8–17.8 GHz). Those properties proved that the composites could act as promising absorbers in the S, C, X, and Ku bands.     

Structural and optical properties of Mg1−xMnxP2O6 (x = 0–1.0) magnesium metaphosphate

Structural and optical properties of Mg_1−xMn_xP₂O₆ (x = 0–1.0) magnesium metaphosphate were investigated in detail. The complete solid solution of MgP₂O₆–MnP₂O₆ is confirmed as monoclinic space group C2/c. The dynamic luminescence was studied by changing the Mn²⁺ content (0–100 mol%) and temperature (10–300 K). There is a good chemical homogeneity in Mg_1−xMn_xP₂O₆ (x = 0–1.0), which can be supported by the linearly varying cell size and the gradually changing vibration spectrum. However, the optical properties of the solid solution do not show a continuous change trend, that is, an obvious inflection point appeared when x = 0.5. Mg_1−xMn_xP₂O₆ (x = 0.1–0.5) shows a dominant O²⁻ → Mn²⁺ charge transfer (CT) absorption in the near UV region and feeble d–d transitions of Mn²⁺ in visible wavelength region. However, Mg_1−xMn_xP₂O₆ (x = 0.6–1.0) presents a strong d–d absorption transition and nearly disappeared CT band. The changing trend of optical absorption is also maintained in the excitation and emission of the solid solutions. In Mg_1−xMn_xP₂O₆ (x = 0.1–0.5), (Mn, Mg)O₆ octahedron has slight distortion, and the effective luminescence only occurs when CT band excitation is used. In contrast, in Mg_1−xMn_xP₂O₆ (x = 0.6–1.0), (Mn, Mg)O₆ octahedron is highly distorted, and only excitation at d–d transition produces effective luminescence. This research highlights the critical role of MnO₆ octahedral distortions in the luminescence properties of Mn²⁺ activators. The research provides a reference for developing optical materials.     

Structure,magnetic and electrical transport properties of the perovskites Sm1−xCaxFe1−xMnxO3

The structure of series Sm_1−xCa_xFe_1−xMn_xO₃ (0.0 ≤ x ≤ 1.0) compounds was investigated. The lattice parameters increase with coupled substitution Sm³⁺ by Ca²⁺ and Mn⁴⁺ for Fe³⁺. The variation of parameter, c, is larger than that of a and b, respectivly. The detailed analysis of magnetic properties of series Sm_1−xCa_xFe_1−xMn_xO₃ (0.1 ≤ x ≤ 0.9) shows that local magnetic interaction between Fe³⁺ and Fe³⁺ and Mn⁴⁺ and Mn⁴⁺ at below magnetic transition temperature is antiferromagnetic. Above magnetic transition temperature the presence of large magnetic cluster is proposed and the sizes of magnetic clusters decrease with Mn⁴⁺. The electrical transport behaviors related with small polaron hopping and variable range hopping models.     

Effect of Ca2+ Substitution on the Structure,Microstructure, and Microwave Dielectric Properties of Sr2Al2SiO7 Ceramic

The effect of Ca²⁺ substitution on the structure, microstructure, and microwave dielectric properties of Sr–gehlenite (Sr₂Al₂SiO₇) ceramic has been investigated. The structure and microstructure of Sr_2?xCa_xAl₂SiO₇ ceramics were analyzed via X‐ray diffraction (XRD) as well as scanning and transmission electron microscopic techniques. While the end‐members (x = 0 and 2) form isostructural compounds, a highly defective, nonstoichiometric, Ca‐rich secondary phase was observed via bright‐field transmission electron microscopy and energy dispersive X‐ray spectroscopy in compositions corresponding to x = 0.75 and 1.5. The concentration of secondary phase in x = 0.75 is too low to be detected via XRD or scanning electron microscopy. Identical selected‐area electron‐diffraction patterns of the compounds (x = 0, 1, and 2) confirmed that they belong to the space group P2₁m (no. 113) with tetragonal crystal symmetry. The porosity‐corrected relative permittivity at microwave frequencies showed a gradual increase with Ca²⁺ content; however, Ca²⁺ substitution made only marginal changes to the microwave dielectric properties except in the case of x = 1.5, in which the secondary phase reduced the quality factor considerably. Thermal conductivity decreased with increasing Ca²⁺ content, and the compounds with defective structures showed the lowest thermal conductivity. All the compounds exhibited low coefficients of linear thermal expansion, with values varying in the range 2.3–3.6 ppm/°C.     

Thermoelectric properties and stability of glasses in the Cu‐As‐Te system

Chalcogenide glasses and more importantly their glass‐ceramics counterparts have been an interesting but very peculiar class of thermoelectric materials, with inherently low thermal conductivity (<0.3 W/m·K). In this study, we report on the fabrication of glasses in the ternary system Cu‐As‐Te (Cu_xAs_55?xTe₄₅ [5≤x≤20], Cu₁₅As_85?yTe_y [45≤y≤70], and Cu₂₀As_80?yTe_y [45≤y≤65]) by melt‐quenching and subsequent spark plasma sintering treatment. Their thermal and structural properties have been studied by differential scanning calorimetry and Raman spectroscopy, leading to give insights into the structural evolution of the glassy matrix. Coupling this information with the analysis of their electrical transport properties allowed us to deepen further our understanding of the compositional effect on their thermoelectric properties, and indirectly how the evolution of their electronic band structure is at play. Despite exhibiting low ZT values by themselves, Cu‐As‐Te glasses may still be interesting candidates for thermoelectricity through partial crystallization for which knowing the relationship between composition and properties remains essential.     

Dielectric Properties of Ba0.8Ca0.2TiO3–Bi(Mg0.5,Ti0.5)O3–NaNbO3 Ceramics

Ceramics in the system 0.45Ba_0.8Ca_0.2TiO₃–(0.55?x)Bi(Mg_0.5Ti_0.5)O₃–xNaNbO₃, x = 0–0.02 were fabricated by a conventional solid‐state reaction route. X‐ray powder diffraction indicated cubic or pseudocubic symmetry for all samples. The parent 0.45Ba_0.8Ca_0.2TiO₃–0.55Bi(Mg_0.5Ti_0.5)O₃ composition is a relaxor dielectric with a near‐stable temperature coefficient of relative permittivity, ε_r = 950 ± 10% across the temperature range 80°C–600°C. Incorporation of NaNbO₃ at x = 0.2 extends the lower working temperature to ≤25°C, with ε_r = 575% ± 15% from temperatures ≤25°C to >400°C, and tan δ < 0.025 from 25°C to 400°C. Values of dc resistivity ranged from ~10⁹ Ω·m at 250°C to ~10⁶ Ω·m at 500°C. The properties suggest that this material may be of interest for high‐temperature capacitor applications.     

Thermoelectric properties of layered Ca3.95RE0.05Mn3O10 compounds (RE = Ce,Nd, Sm,Eu, Gd,Dy)

In this work, polycrystalline samples of the substituted n = 3 Ruddlesden-Popper Ca_4−xRE_xMn₃O₁₀ phase were prepared by solid-state reaction (RE, rare earth = Ce, Nd, Sm, Eu, Gd, Dy). Single phased samples were synthesized for sintering times larger than 150 h at 1350 °C. Complete thermoelectric characterizations were performed from 5 to 390 K, in terms of electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ). As expected, the substitution of Ca by different rare earth elements leads to a significant modification of the thermoelectric properties. With substitution level as low as 1.25 at.%, a remarkable decrease of the electrical resistivity is observed. The influence of this cationic substitution on the thermal conductivity (κ), Seebeck coefficient (S), and the figure of merit ZT is also discussed. In this study, the best one reaches 5.8 × 10⁻³ at 300 K for the Ca_3.95Eu_0.05Mn₃O₁₀ composition, a value 6 times higher than the ZT exhibited by the beginning Ca₄Mn₃O₁₀ sample.     

Enhanced magnetism in Ru-doped hybrid improper perovskite Ca3Mn2O7 via experimental and first-principles study

The quasi-2D Ruddlesden–Popper layered perovskites with single-phase multiferroicity have attracted much attention in recent magnetoelectric memory applications. We have systematically investigated the optical and magnetic properties of Ru-doped hybrid improper perovskite Ca₃Mn₂O₇ both experimentally and using first-principles calculations. The Ca₃Ru_xMn_2−xO₇ (x = 0, 0.02, 0.06, 0.10) powders were successfully synthesized using the sol–gel method. Ru doping enhanced the ferromagnetism of Ca₃Mn₂O₇. The quasi-2D antiferromagnetic (AFM) fluctuation effect was observed in Ca₃Mn₂O₇ and in certain doped samples. We also found that the optical bandgaps of the doped samples were reduced after doping, agreeing with the results of the first-principles calculations. Infrared absorption spectra indicated the distortion of the Mn–O bonds was possibly due to the Jahn–Teller effect. To analyze the electronic structures and to understand the detailed atomic contributions of magnetic moments, the Crystal Orbital Hamilton Population (COHP) and Integrated COHP of the (Mn,Ru)O₆ octahedra were also calculated. The Ru-doped materials with the coexistence of ferromagnetic and AFM orderings are expected to be excellent candidates for magnetoelectric devices.     

Sol-gel synthesis,microstructure, and thermoelectric properties of Ca2.8-xBixDy0.2Co4O9+δ

Small-sized Ca_2.8-xBi_xDy_0.2Co₄O_9+δ (0 ≤ x ≤ 0.1) powders with a plate-like morphology were synthesized via the citric acid-assisted sol-gel method. The structural and thermoelectric properties of Ca_2.8-xBi_xDy_0.2Co₄O₉ samples were studied with an emphasis placed on the Bi content and the fabrication process. The as-sintered Ca_2.8-xBi_xDy_0.2Co₄O₉ samples exhibited a single Ca₃Co₄O_9+δ phase and a plate-like morphology. With increased Bi content, the grain size of the sintered Ca_2.8-xBi_xDy_0.2Co₄O₉ samples decreased, whereas the density of the sintered Ca_2.8-xBi_xDy_0.2Co₄O₉ samples increased. The incorporation of Bi up to x = 0.075 yielded high electrical conductivity. Meanwhile, the Seebeck coefficient decreased with increases in Bi content. The largest power factor (2.18 × 10⁻⁴ W m⁻¹ K⁻² at 800 °C) was obtained for the twice-sintered Ca_2.725Bi_0.075Dy_0.2Co₄O₉. The partial substitution of Bi for Ca and the twice sintering were a highly effective route for improving the thermoelectric properties of Ca_2.8Dy_0.2Co₄O₉.     

The relationship between crystal structure and modified microwave dielectric properties of Ca3SnSi2-xGexO9 ceramics

Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.8) and (1–y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid-state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge⁴⁺ replaced Si⁴⁺, and Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge⁴⁺ substitution for Si⁴⁺ decreased the sintering temperature of Ca₃SnSi_2-xGe_xO₉ from 1425 to 1300°C, the SnO₆ octahedral distortions, and the average CaO₇ decahedral distortions, which affected the τ_f value. The large average decahedral distortions corresponded with nearer-zero τ_f values at Ca₃SnSi_2-xGe_xO₉ (0.1 ≤ x ≤ 0.4) ceramics. The τ_f value and sintering temperature of Ca₃SnSi_2-xGe_xO₉ (x = 0.4) ceramic were adjusted to near-zero by CaSnSiO₅ and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: ε_r = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τ_f = ‒5.8 ppm/°C.