Sintering,micro-structure and Li+ conductivity of Li7−xLa3Zr2−xNbxO12/MgO (x = 0.2–0.7) Li-Garnet composite ceramics

Nb-doped Li₇La₃Zr₂O₁₂ (Nb-LLZO) is one of the promising electrolyte candidates in the Li-Garnet family due to its high Li-ion conductivity. The sintered Nb-LLZO ceramics, however, often exhibit abnormal grain growth with high porosity and poor mechanical properties. For advantaged electrochemical and mechanical properties, a uniform and dense microstructure is desired. In this research, MgO has been added as a secondary phase to inhibit abnormal grain growth in Nb-LLZO. The sintering process of the Nb-LLZO/MgO composite ceramics has been studied for different Nb doping levels (0.2–0.7 pfu) at sintering conditions of 1250?°C for 1–360?min. The ceramic density, microstructure, and Li-ion conductivity are reported. The composite ceramics have shown a very fast sintering speed. At 1250?°C, the 0.4Nb-LLZO/MgO composite can be well-sintered in 1?min. For sintering at 1250?°C for 40?min, ceramic samples showing relative density of 97%, conductivity of 6?×?10^?4 S?cm^?1 at 25?°C, and activation energy of 0.40?eV are obtained.     

Structural,morphological and mechanical insights from La2O3 doped machinable silicate glass ceramics for biomedical applications

Machinable glass ceramics attracted much attention in recent years due to its improved mechanical and therapeutic performances. La₂O₃ doped SiO₂–Al₂O₃–MgO–K₂CO₃–CaO–MgF₂ glass and glass ceramics (GCs) were synthesized using melt-quenching and solid-state reaction methods. Herein, doping impact of La₂O₃ on physical, optical, morphological, mechanical, and biological properties were studied. XRD reveals the major phase formation of monoclinic cuspidine, Ca₄F₂Si₂O₇ with some minor phases. 3 mol% of La₂O₃ GCs shows a new major crystalline phase of akermanite, Ca₂MgSi₂O₇. FTIR study shows that La₂O₃ acts as a network modifier and non-bridging oxygens presented in the glassy structure tends to be increased. Optical band gap and particle size were lies in the range of 4.18–4.10 eV, and 50–57 nm, respectively. Rod-like morphology and their elemental distributions were confirmed via SEM and EDS techniques. TEM studies suggested that the lattice planes agreed with the XRD results and confirmed a major phase formation of Ca₂MgSi₂O₇. Enhanced mechanical properties were observed using Universal Testing Machine. The cell viability and cell cytotoxicity, were performed by MTT and ALP assay.     

Two step sintering of a novel calcium magnesium silicate bioceramic: Sintering parameters and mechanical characterization

Two-step sintering (TSS) was applied to control the grain growth during sintering of a novel calcium magnesium silicate (Ca₃MgSi₂O₈ – Merwinite) bioceramic. Sol–gel derived nanopowders with the mean particle size of about 90 nm were sintered under different TSS regimes to investigate the effect of sintering parameters on densification behavior and grain growth suppression. Results showed that sintering of merwinite nanopowder under optimum TSS condition (T₁ = 1300 °C, T₂ = 1250 °C) yielded fully dense bodies with finest microstructure. Merwinite compacts held at T₂ = 1250 °C for 20 h had the average grain size of 633 nm while the relative density of about 98% was achieved. Mechanical testing was performed to investigate the effect of grain growth suppression on the hardness and fracture toughness. Comparison of mechanical data for samples sintered under two sintering regimes, including TSS and normal sintering (NS), showed TSS process resulted in significant enhancement of fracture toughness from 1.77 to 2.68 MPa m^1/2.     

Experimental determination of phase equilibria in the CaO-BaO-SiO2-12 mol pct. Al2O3-13 mol pct. MgO system at 1573 K and 1623 K

Phase equilibria of the CaO-BaO-SiO₂-12mol pct. Al₂O₃-13mol pct. MgO system with a wide substitution range of CaO with BaO have been experimentally determined at 1623 K (1350°C) and 1573 K (1300°C) using high-temperature equilibration followed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) analysis. The (Ca,Ba)₃MgSi₂O₈, BaAl₂O₄, BaAl₂Si₂O₈ and Ca₂(Al_0.46Mg_0.54)(Al_0.46Si_1.54)O₇ phases have been designated within the phase diagram. The liquidus temperature initially decreased and then increased for the samples substituting CaO with BaO at a constant (C + B)/S ratio between 1.50 and 1.86. For samples with a constant BaO/CaO ratio, the liquidus temperature showed similar trends with a lower (C + B)/S ratio from 1.22 to 0.67. The volume fraction of crystal phases of the samples as-quenched from 1573 K (1300°C) correlated well with the variation of liquidus and the primary phases. In addition, the change in the Gibbs free energy of the reactions and the bond parameter (X_p × Z/R_k) of the cations were analyzed, where the maximum change in the Gibbs free energy was found for the formation of Ca₃MgSi₂O₈; furthermore, the stronger basic tendency of Ba²⁺ than Ca²⁺ facilitates Ba²⁺ substitution for Ca²⁺ and bonding with acidic tendency cations to form Ba-containing phases.     

Effect of Sr and Ca substitution of Ba on the photoluminescence properties of the Eu2+ activated Ba2MgSi2O7 phosphor

The effects of Sr and Ca substitution of Ba on the Ba_1.98-xSr_x(Ca_x)MgSi₂O₇:Eu²⁺ photoluminescence properties have been investigated. The physical mechanisms for the photoluminescence variations are discussed. With Rietveld refinement method, the crystal structure of Ba_1.98MgSi₂O₇:0.02Eu²⁺ and the lattice parameters of Sr and Ca substituted phosphors were refined. The emission band shift, the photoluminescence intensity variation, the phosphor chromaticity evolution, the Eu²⁺ lifetime distribution and the thermal stability elevation were investigated. With Sr and Ca substitution, the cell is shrinks. The cell shrinkage is resulting in the increase of the Eu²⁺ 5d electron crystal field splitting intensity, which is the reason for the emission band shift towards the long wavelength band. The photoluminescence intensity is increased firstly and then decreased. The intensity variation is the competitive result between the increase of the crystal structure rigidity and the rise of the lattice defect. The correlated color temperature can be cut down and the color purity can be adjusted. The photoluminescence life time of Eu²⁺ is raised firstly and then decreased. For Sr and Ca substitution, the thermal stability can be elevated. With the forbidden band gap calculation, the reason for the thermal stability elevation was investigated that for the substituted phosphors the forbidden band gap is enlarged and then limits the Eu²⁺ 5d self-ionization from the splitting levels to the conduction band. This work reveals that the Sr and Ca substitution of Ba can elevate the Ba_1.98-xSr_x(Ca_x)MgSi₂O₇:Eu²⁺ photoluminescence properties and improve the applications for the White Light Emitting Diode.     

Preparation of mullite whiskers from kaolin via the addition of tribasic calcium phosphate

Mullite whiskers are potential candidates for improving the mechanical and thermal properties of ceramic, glass, and composite material. In this work, well‐developed whisker‐shaped mullite has been produced by adding tribasic calcium phosphate (Ca₃(PO₄)₂) into kaolin before calcining in air. In the raw kaolin, rod‐like mullite crystal of ~0.5‐1.0 μm length and ~0.05‐0.2 μm diameter formed at 1350°C, and mullite whiskers were not be observed; however, by doping 6 wt% Ca₃(PO₄)₂ into kaolin, mullite whiskers of ~5.5 μm length and ~0.05‐0.10 μm diameter grew at 1250°C. The formation of high aspect ratio of mullite whiskers can probably be explained by the synergistic effect of P₂O₅ and CaO, resulting in the formation of liquid phase with a relatively higher content of Si and a lower viscosity at low temperature of 1250°C, which facilitates the growth of mullite displaying acicular morphology. The results are of interest in producing high aspect ratio of mullite whiskers from kaolin at reduced calcination temperatures.     

Sintering of LaCoO3 based ceramics

The densification, microstructure and phase evolution of near stoichiometric, Co-excess and Co-deficient perovskite La_1−xM_xCoO_3−δ (M=Ca, Sr; x=0, 0.2) powders have been investigated by electron microscopy and powder X-ray diffraction. Sub-micron powders were prepared from nitrate precursors using the glycin-nitrate and the EDTA methods. The sintering temperature was observed to decrease with Ca or Sr substitution. Dense materials with grain size in the order of 3–5 μm have been obtained at 1200°C for near stoichiometric powders. Considerable grain growth was observed at higher sintering temperatures. The presence of other crystalline phases in addition to the perovskite due to Co-excess/-deficiency considerably affects the microstructure and acts as grain growth inhibitors by grain boundary pinning. The volume fraction of secondary phases is particularly large in the case of Co-deficient LaCoO₃ due to the formation of La₄Co₃O₁₀. In non-stoichiometric La_0.8Ca_0.2CoO₃, a liquid phase consisting mainly of CaO and CoO was observed at 1400°C causing exaggerated grain growth. Considerable pore coarsening was observed in Co-excess La_0.8Ca_0.2CoO₃ at 1350°C. The present investigation demonstrates the importance of controlling the stoichiometry of LaCoO₃ based ceramics in order to obtain dense materials with well defined microstructure.     

Enhancement of the densification and thermal properties of Ca2Mg2Al28O46 ceramic by MnO addition

Ca₂Mg₂Al₂₈O₄₆ consists of platelet or platelet-like structural features derived from CaAl₁₂O₁₉. However, its application in dense structural materials is limited due to its poor sinterability and loose structure. In this work, Ca₂Mg₂Al₂₈O₄₆ ceramic was fabricated by solid-state reaction sintering, and the effects of MnO addition on the densification and thermal properties were investigated at 1600-1750 °C. The results showed that the Mn²⁺ solid dissolved into the Ca₂Mg₂Al₂₈O₄₆ lattice by the isovalent substitution of Mg²⁺ at 1650 °C, causing the grain morphology to change from hexagonal to equiaxed and resulting in a distorted magnetoplumbite structure. At 1700 °C, the solid solution reaction accelerated the densification, with the apparent porosity decreasing from 32.5% to 8.4% when 3 wt% MnO is added, promoted grain growth and pore discharge by increasing the number of lattice defects, grain boundary migration rate and in-situ stress. The enhanced thermal expansion coefficient and thermal conduction were mainly due to lattice expansion and grain coarsening. Moreover, the formation of trace amount of the secondary phase Mg_1-xMn_xAl₂O₄ also contributed to the improvement in the thermal properties.     

Structural,magnetic and dielectric properties of Co-Zr substituted M-type calcium hexagonal ferrite nanoparticles in the presence of α-Fe2O3 phase

Polycrystalline nanoparticles of M-type Ca(ZrCo)_xFe_12?2xO₁₉ (0.0?≤?x?≤?1.0) hexaferrites were prepared using a simple heat treatment method at a low heating temperature of 650?°C. Effect of cobalt-zirconium substitution on the structural, microstructural, magnetic and dielectric properties was investigated. XRD analysis indicates that all the samples possess a hexagonal structure with anti-ferromagnetic α-Fe₂O₃ phase. The values of lattice parameters and cell volume found to be increased with increasing the cobalt-zirconium substitution along with the amount of α-Fe₂O₃ phase. Crystal symmetry has not affected by Zr–Co substitution in prepared calcium hexaferrite samples but the position of diffraction peak [108] is found to shift towards a lower angle as an increase in the substitution of Zr–Co. The crystallite size found to vary between 12 and 17?nm. SEM images show agglomerated grains and surface morphology has changed with Zr–Co substitution. EDX analysis of typical samples revealed the presence of Ca, Fe, Co, Zr. The magnetic analysis revealed the formation of multi-domain structure. Room temperature Mössbauer spectra of prepared samples show that all five sextets are merged together with a paramagnetic doublet and it confirmed that the size of particles is very small in the nano range. Single and double semicircle arcs were observed in Cole-Cole plots, due to the contributions of grain and grain boundaries resistance.     

Sintering behavior and mechanical properties of hydroxyapatite ceramics prepared from Nile Tilapia (Oreochromis niloticus) bone and commercial powder for biomedical applications

In this work, Nile tilapia (Oreochromis niloticus) bone was calcined at 800 °C for 5 h in an air atmosphere to obtain hydroxyapatite powder (FB powder). The elemental composition, phase structure, and morphology of the FB powder were investigated and compared with commercial hydroxyapatite powder (SM powder). The FB-powder exhibited 1.01 at. % of Mg while the SM-powder showed Mg in ppm-level. Carbonate groups were detected in the two powders. Both HAp and β-tricalcium phosphate (β-TCP) structures were found in the FB powder, but the SM powder exhibit only the HAp phase. Irregular-shaped particles were observed in the FB powder. After the two HAp powders were sintered at 1200 °C and 1250 °C for 2 h (FB-1200, FB-1250, SM-1200, and SM-1250), the β-TCP intensity peaks of the FB-ceramic samples significantly increased with increasing sintering temperature. The highest relative density, well-packed grains, and β-TCP stabilization by Mg at the Ca5 site of the FB-1250 structure were the dominant factors governing the highest mechanical properties. Although high density was observed in the SM-1200 sample, Vickers hardness of the SM-1200 sample is lower than the FB-1250 sample. This may be attributed to the partial decomposition of HAp into β-TCP, α-tricalcium phosphate (α-TCP), and Ca₁₀(PO₄)₆O phases. In addition, the increase of grain size was the main factor that governs the increasing compressive strength and Young's modulus instead of density and phase decomposition of the SM-ceramic samples.     

Effect of Yb2O3 and TiO2 on reaction sintering and properties of magnesium aluminate spinel

Magnesium aluminate spinel with an initial MgO: Al₂O₃ molar ratio of 2:1 was prepared from its constituent oxides through a solid-state sintering process at temperatures ranging from 1550 to 1700 °C in a normal air atmosphere. The effect of varying amount (0.25–1.0 wt%) of TiO₂ and Yb₂O₃ on densification, phase assemblage, mechanical, thermo-mechanical properties and microstructure of magnesia-rich spinel were investigated under static heating condition. The addition of TiO₂ and Yb₂O₃ favours the densification of magnesia-rich spinel, which is discernible up to 1650 °C. This beneficial effect may be attributed to the development of the secondary phase and formation of solid solution due to the dissolution of the additive ions in the spinel structure. A marginal increase in the average grain size of the samples along with a narrower grain size distribution occurred with the incorporation of both the additives. Both the additives improved the mechanical properties of the magnesia-rich spinel; however, better room temperature flexural strength was achieved with Yb₂O₃ as compared to TiO₂ addition. For the samples sintered at 1550 °C, 1.0 wt% Yb₂O₃ addition resulted in 30% increase in flexural strength; however, same amount of TiO₂ addition increased the strength by 20%. In case of thermal shock resistance, 1.0 wt% TiO₂ and 0.25 wt% Yb₂O₃ addition demonstrated promising result among all the samples.     

The influence of MgO on the crystallization behaviour and properties of SrO-rich phosphosilicate glasses

A series of glass was produced to investigate the effect of MgO/SrO replacement on the crystallization characteristics and properties of phosphosilicate glasses containing high SrO content. The glass samples were synthesized by conventional melting technique based on 5CaO-(40-X)SrO-X MgO– 43SiO₂–7P₂O₅–5CaF₂ (where; X = 10, 20, 30 and 40 mol%). The influence of MgO/SrO replacement on phase assemblages, microcrystalline structures, thermal expansion, and mechanical properties was examined as a function of basic chemical compositions and crystallization parameters. Predominant strontium meta-silicates together with strontium fluoroapatite phases are crystallized from the base glass free of magnesium. The substitution of strontium by magnesium up to 50% led to formation strontium akermanite phase Sr₂MgSi₂O₇ at the expense of SrSiO₃ phase. Whereas the increase of the MgO/SrO of more than 50%, which led to the crystallization of the clino-enstatite MgSiO₃ as a predominant phase. The results show that the α-values of the glass-ceramics are ranged in 94–125 × 10⁻⁶ K⁻¹ over the temperature range (25–500 °C). On the other hand, MgO/SrO replacements led to enhancing the microhardness of the resultant crystalline materials from 4713 Mpa to 6744 Mpa. As a result of the designed glass compositions, promising crystalline phases were obtained as well as good thermal and mechanical properties for the resultant glass-ceramics. Therefore, the designed glass-ceramics can be strongly used as biomaterials especially for bone reconstruction applications.     

Densification of copper oxide doped alumina toughened zirconia by conventional sintering

The effect of copper oxide doping (0.05–1 wt%) on the densification, microstructure evolution and mechanical characteristics of alumina toughened zirconia (ATZ: 80 wt% Y-TZP + 20 wt% Al₂O₃) ceramic composites was investigated. Green samples were pressureless sintered using a short hold time of 12 min at temperatures varying from 1250 °C to 1500 °C. The incorporation of up to 0.2 wt% copper oxide was beneficial in promoting densification at low sintering temperature and improving the mechanical properties of ATZ without affecting the tetragonal phase stability. It was found that 0.2 wt% copper oxide addition was most efficacious, and the samples could attain a relative density of approximately 92% at 1250 °C, approximately 97% dense at 1350 °C and above 99% dense at 1450–1500 °C. This approach was also accompanied by an improvement in the Vickers hardness (12.7 GPa) and fracture toughness (6.94 MPam^1/2) when consolidated at 1450 °C/12 min. In comparison, the undoped composite exhibited relative densities of approximately 80% at 1250 °C, 87% at 1350 °C and approximately 97%–98% at 1450 °C-1500 °C. However, the study also found that higher dopant levels (0.5 wt% and 1 wt%) was not beneficial because the tetragonal zirconia phase was disrupted upon cooling from sintering, resulting in the monoclinic phase formation. In addition, low densification and poor mechanical properties were obtained.     

Phase development in ZnO varistors

Based on a typical ZnO varistor composition (97·0 mol.-% ZnO, 1·0 mol.-% Bi₂O₃, 1·0 mol.-% Sb₂O₃, 0·5 mol.-% MnO and 0·5 mol.-% Co₃O₄), phase development of the ZnO varistor during sintering has been investigated using in situ high temperature X-ray diffraction up to 900°C, and conventional ambient X-ray diffraction for samples sintered at 900°C to 1250°C. The results indicate that α-Bi₂O₃ can be detected until 700°C; the pyrochlore phase can be detected in the samples heat treated at 700°C and up to 1250°C; the spinel phase is present at and >900°C. However, the main phases in the varistor are established by 950°C. By this temperature, the essential microstructure features are formed, and the varistors exhibit non-linear electrical properties, with a non-linear coefficient α of 35 and breakdown field of 8000 V cm^?1. With increasing sintering temperature, both the α value and breakdown field decrease.     

Investigation of ferroelectric,piezoelectric and mechanically coupled properties of lead-free (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 ceramics

Lead-free piezoelectric ceramic (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) has been synthesised by solid-state sintering method and the effect of grain size on ferroelectric, piezoelectric, dielectric, mechanical and piezo-electro-mechanical properties was systematically studied. The compacted powders were sintered at three temperatures i.e. 1450°°C, 1500°C and 1550°C for an optimised duration of 5?h and they have exhibited well resolved morphotropic phase boundary with an average grain size ranging from 10 to 25?µm. Enhanced piezoelectric charge, d₃₃ ～ 560 pC/N and voltage, g₃₃ ～ 14.3?mV?m/N coefficients were obtained for the 1450°C sintered BCZT sample. A maximum strain of around ～0.14% was obtained which is comparable to that of lead-based piezoelectrics. Variation of relative permittivity with temperature revealed that the curves are independent of frequency, indicating the typical relaxor ferroelectric nature of the samples. A systematic study on cyclic loading was performed to evaluate piezo-electro-mechanical coefficients at different loads which showed hysteresis behaviour. High value of elastic modulus (E) and hardness (H) i.e. 262.7?±?38.1?GPa and 13.7?±?1.7?GPa were exhibited by samples sintered at 1450°C, which is higher than that of BCZT synthesised by wet-chemical methods. The results are discussed.     

Effect of annealing on grain growth and Y segregation behavior in tetragonal ZrO2 thin film

In order to fabricate tetragonal yttria stabilized zirconia samples with large grain size, 3 mol% Y₂O₃ doped zirconia thin films were grown on (0001) α-Al₂O₃ substrate by pulsed laser deposition (PLD) followed by subsequent high temperature annealing. The thin film samples were annealed at 1200°C, 1250°C, 1300°C, and 1350°C in order to obtain larger grain size without Y segregation. The microstructure and chemical composition of these annealed films were analyzed using atomic force microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The as-grown thin film was found to be composed of [111]-oriented grains of ∼100 nm connected with small-angle tilt boundaries. Based on analysis of annealed thin films, it was revealed that grain growth of tetragonal zirconia occurred anisotropically. Cross section scanning transmission electron microscopy observations revealed that such grain growth behavior is affected by the step-terrace structures of the sapphire substrate. Energy-dispersive X-ray spectroscopy showed that Y was found to distribute almost uniformly below 1300°C but to segregate at the grain boundaries at 1350°C. As a conclusion, the 1300°C-annealed sample shows the largest grain size with homogeneous Y distributions.     

Effect of thermal exposure on the microstructure and strength of an alumina-silica ceramic fiber

The microstructure and mechanical properties of an alumina-silica ceramic fiber after thermal exposure at 1100–1300°C were investigated by X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy analyses and room temperature tensile strength test. The results showed that the fiber was composed of γ-A1₂O₃ and amorphous SiO₂. A phase reaction of γ-A1₂O₃ and amorphous SiO₂ occurred when thermal exposure temperature exceeded 1150°C, and a new mullite phase formed. The grain size of the newly formed mullite increased with the increase of exposure temperature. Both the phase transition and grain growth of mullite had a significant impact on the mechanical properties of the fiber. Tensile strength of the fiber decreased slightly when thermal exposure temperature was below 1150°C, while the strength retention of the fiber decreased sharply to 65.36% as exposure temperature rose to 1200°C. A higher dispersion of tensile strength was also observed at higher exposure temperatures, as revealed by the Weibull statistical model.     

Inorganic-salt coprecipitation synthesis,fluoride-doping,bioactivity and physiological pH buffering evaluations of bredigite

Bredigite (Ca₇MgSi₄O₁₆), with suitable bioactivity, biodegradation, biocompatibility and mechanical properties, is a promising candidate for the repair and regeneration of damaged bone tissues. In this research, for the first time, bredigite was synthesized by a facile and inexpensive coprecipitation method using inorganic salt precursors, followed by calcination at 1200 °C. Additionally, 0.5 mol% fluoride was successfully doped into the structure without the formation of any second phases. X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the formation of single-phase orthorhombic bredigite in the samples and the incorporation of fluoride in the doped sample, respectively. Both the undoped and doped samples exhibited apatite-formation ability in terms of the precipitation of hydroxycarbonate apatite when exposed to a simulated physiochemical medium, with an increase in this characteristic as a result of fluoride doping. The addition of fluoride also lowered and buffered the pH value of the medium, where the enhancement of this parameter is due to the fast bioresorption of bredigite affecting disadvantageously biocompatibility.     

Plasma-sprayed La2Ce2O7 thermal barrier coatings against calcium–magnesium–alumina–silicate penetration

As one of promising thermal barrier coating (TBC) candidates, La₂Ce₂O₇ (LC) has attracted increasing attention because of its low thermal conductivity and potential capability to be operated above 1250 °C. In this paper, the microstructure evolution and mechanical properties of the plasma-sprayed LC TBC with calcium–magnesium–alumina–silicate (CMAS) glassy deposits at 1250 °C were investigated. Due to chemical reaction between the CMAS deposits and LC coating, a dense sealing layer, mainly composed of Ca₂(La_xCe_1−x)₈(SiO₄)₆O_6−4x and CeO₂, was formed on the coating after heat-treatment at 1250 °C and effectively prevented CMAS from further penetration. The interaction layer had the micro-hardness of ∼10–12 GPa, relatively harder than the LC coating.     

Effect of substrate on the microstructure and thermoelectric performances of Sr-doped Ca3Co4O9 thick films

Ca₃Co₄O₉ thermoelectric materials in form of thick films are very promising in practical applications due to their low costs and relatively high performance. In this work, two different suspensions have been used to produce different coatings on Al₂O₃ polycrystalline substrates with theoretical green thickness of 360 and 2000?µm. Moreover, the effect of substrate has also been investigated using Al₂O₃ monocrystalline substrates and a 360?µm green thickness. Sintering procedure at 900?°C for 24?h has drastically decreased coating thickness. XRD performed on the coatings surface has shown the formation of small amounts of Ca₃Co₂O₆ secondary phase on the polycrystalline substrates, while it was more abundant, and accompanied by Ca₂Co₂O₅ on the monocrystalline substrates. In spite of the higher secondary phases content, monocrystalline substrates produced a slight grain orientation which led to the highest thermoelectric properties between the samples (0.38?mW/K²m at 800?°C), and very close to the best reported values in the literature.