Increase Of Grain Boundary Resistance Research Articles

Microstructures and complex impedance analysis of spray pyrolysis-synthesized Ni doped ZnO for optoelectronic applications

This study focuses on the physical exploration, particularly examining the structural and electrical attributes of ZnO thin films produced through spray deposition, with variations in the Ni/Zn ratio (0.25 %, 0.5 %, and 0.75 %). X-ray diffraction (XRD) analysis reveals that both undoped and Ni-doped ZnO films exhibit a hexagonal crystalline structure, with a preferred orientation along the (002) direction perpendicular to the substrate. The semiconductor nature of all prepared compounds is confirmed by the grain boundary resistance. An escalation in Ni concentration corresponds to an increase in grain boundary resistance. The activation energy values, derived from both relaxation time and grain boundary resistances, closely align. Impedance studies indicate the presence of two relaxation processes within the compounds. The Nyquist diagram illustrates the emergence of semicircles, with decreasing radii at higher temperatures, indicating thermally activated semiconductor behavior in these samples, as evidenced by electrical conductance and distribution of relaxation times.

Role of mixed oxidant and controlled oxygen partial pressure heat treatment to regulate the dielectric properties and resistivity of SrTiO3-based CP ceramics

Sr0.99La0.01TiO3 (SLT10) colossal permittivity (CP) ceramic materials were synthesized using solid phase method and secondary heat treated using mixed oxidant 35%Bi2O3–10%Al2O3–20%MgO–25%CuO–10%SiO2 oxidant. The heat treatment atmospheres were chosen as O2, air, and Ar to correspond to different oxygen partial pressures. The dielectric properties of the Sr0.99La0.01TiO3-Percolated (SLT10-P) ceramics were investigated, and the contribution of the oxidant to the resistivity enhancement was verified by complex impedance spectroscopy and DC resistivity tests. Excellent dielectric properties were obtained for SLT10-P Air ceramic sample (16543 for dielectric permittivity and 0.016 for loss tangent), and the resistivity was increased from 2.13 × 108 Ω cm (SLT10) to 1.23 × 1011 Ω cm (SLT10-P Air). The resistance degradation mechanism of SLT10-P ceramics and oxygen vacancy migration in the process of resistance degradation were studied by using resistance monitoring device and thermally stimulated depolarization currents (TSDC) test. The introduction of oxidant optimizes the temperature stability and resistivity of SLT10 ceramics, but it will lead to the decrease of dielectric permittivity. The atmosphere of heat treatment changed the concentration of oxygen vacancy in ceramics. When SLT10-P O2 was treated in O2 atmosphere, the concentration of oxygen vacancy in ceramics decreased, which led to the decrease of dielectric permittivity and the increase of grain boundary resistance. For SLT10-P Ar ceramic, more oxygen vacancies and free electrons are induced by low oxygen partial pressure heat treatment, which enhances the dipole effect of electron pinning defects and leads to colossal dielectric permittivity, but high concentration of oxygen vacancies will affect the resistance decline. In SLT10-P Air ceramic, the coexistence of colossal permittivity and low loss tangent and high resistance is realized.

Phase Evolution, Dielectric, and Electric Behavior of Sm‐Doped BCTO Ceramic Fabricated by Semi‐Wet Method

AbstractBi(2/3)‐xSmxCu3Ti4O12 (BSCTO x = 0.05, 0.10, and 0.20) ceramics are synthesized using semi‐wet technique and an extensive investigation into their structural, morphological, and elemental properties, alongside dielectric and impedance behaviors, is meticulously carried out. X‐ray powder diffraction analysis unequivocally confirmed the formation of a monophasic BCTO cubic phase without any discernible secondary phases. and the crystallite size of the BSCTO ceramic, obtained by X‐ray diffraction using Debye Scherrer formula, range from 62 to 81 nm. Rietveld analysis reveals that ceramics have a body centered cubic structure with space group Im‐3. The Scanning electron microscope image displays the dense microstructure of the ceramics, while EDX analysis unveils the elemental composition of resulting products. Doping with Sm3+ induced a notable reduction in grain size, as observed through Scanning electron microscope and Atomic Force Microscope analyses, indicating Sm3+ hindered grain growth during sintering, potentially resulting in reduced dielectric constant (ε′). Dielectric constant and dielectric loss of the composition (x = 0.2) are found to be 152 and 0.04, respectively at room temperature (1 kHz). Impedance characteristics revealed a substantial increase in grain boundary resistance, leading to improved dielectric loss. The AC conductivity of BSCTO ceramics exhibited a frequency‐dependent increase satisfying to Johncher's power law.

High resistivity under colossal permittivity SrTiO3 based ceramic via controlling ion diffusion

High-performance Sr0.99La0.01TiO3 ceramics were synthesized using a conventional solid-phase method, and Sr0.99La0.01TiO3 percolated (SLT10-P) samples with excellent resistivity were obtained by coating with an oxidant and heat treatment. In this work, simultaneous excellent dielectric properties (16667 of dielectric permittivity, 0.016 of loss tangent at 1 kHz) and high resistivity (1.44 × 1011 Ω·cm at DC100V) was achieved in SLT10-P ceramics at room temperature by modulating the duration of thermal treatment. X-ray Diffraction and scanning electron microscope analyses proved the diffusion of the oxidant in the grains and grain boundaries during the heat treatment. The increase in grain boundary resistance is mainly due to the fact that the insulating layer formed by the oxide ions entering the grain boundary hinders the long-range movement of electrons. In addition, the diffusion of oxygen from the air into the ceramic during the heat treatment process also contributes to the insulation of grain boundaries.

Exceptional dielectric and varistor properties of Sr, Zn and Sn co-doped calcium copper titanate ceramics.

Calcium copper titanate (CCTO) powders associated with the chemical formula Ca1-x Sr x Cu3-y Zn y Ti4-z Sn z O12 (where x, y, z varying from 0 to 0.1) were synthesized via a solid-state reaction route. Dense ceramics (>96% of theoretical density) were obtained by sintering these powders comprising micrometer-sized grains at appropriate temperatures. X-ray powder diffraction studies confirmed the formation of monophasic CCTO cubic phase, with no traceable secondary phases present. The lattice parameter 'a' was found to increase on increasing the dopant concentration. The microstructural studies performed on these ceramics confirmed a decrease in mean grain size (18 μm to 5 μm) with the increase in Sr, Zn and Sn doping concentrations as compared to that of undoped CCTO ceramics though they were sintered at the same temperature and duration (1100 °C/15 h). The dielectric studies (dielectric constant (ε') and the dielectric loss (D)) conducted in a wide frequency range (102-107 Hz) demonstrated an increase in ε' and a decrease in D on increasing the doping concentration. Impedance analysis (Nyquist plots) performed on these ceramics revealed a significant increase in grain boundary resistance. The highest value of grain boundary resistance (6.05 × 108 Ω) (in fact this value was 100 times higher than that of pure CCTO) was obtained for the composition corresponding to x = y = z = 0.075 and intriguingly the ceramic pertaining to this composition exhibited enhanced ε' (1.7 × 104) and lower D (0.024) at 1 kHz. Further, these co-doped CCTO ceramics exhibited substantial improvement in breakdown voltages and nonlinear coefficients (α). The temperature independent (30 -210 °C) dielectric response of these samples qualifies them to be suitable dielectric materials for the fabrication of multilayer ceramic chip capacitors.

Influence of microstructure and crystalline phases on impedance spectra of sodium conducting glass ceramics produced from glass powder

Crystallization of highly ionic conductive N5 (Na5YSi4O12) phase from melted Na3+3x-1Y1-xPySi3-yO9 parent glass provides an attractive pathway for cost-effective manufacturing of Na-ion conducting thin electrolyte substrates. The temperature-dependent crystallization of parent glass results in several crystalline phases in the microstructure (N3 (Na3YSi2O7), N5 and N8 (Na8.1Y Si6O18) phases) as well as in rest glass phase with temperature dependent viscosity. The electrical properties of dense parent glass and of compositions densified and crystallized at 700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C are investigated by impedance spectroscopy and linked to their microstructure and crystalline phase content determined by Rietveld refinement. The parent glass has high isolation resistance and predominantly electrons as charge carriers. For sintering at ≥ 900 °C, sufficient N5 phase content is formed to exceed the percolation limit and form ion-conducting pathways. At the same time, the highest content of crystalline phase and the lowest grain boundary resistance are observed. Further increase of the sintering temperature leads to a decrease of the grain resistance and an increase of grain boundary resistance. The grain boundary resistance increases remarkably for samples sintered at 1100 °C due to softening of the residual glass phase and wetting of the grain boundaries. The conductivity of fully crystallized N5 phase (grain conductivity) is calculated from thorough impedance spectra analysis using its volume content estimated from Rietveld analysis, density measurements and assuming reasonable tortuosity to 2.8 10−3 S cm−1 at room temperature. The excellent conductivity and easy processing demonstrate the great potential for the use of this phase in the preparation of solid-state sodium electrolytes.

Ge4+ doped CaCu2.95Zn0.05Ti4O12 ceramics: Two-step reduction of loss tangent

CaCu3Ti4O12 ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu3Ti4O12 with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 103 to 3.93 × 104 Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu3Ti4O12 ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge4+ dopant into the Zn2+-doped CaCu3Ti4O12 ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 105 Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 104). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu3Ti4O12 structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors.

Enhanced dielectric properties of Ca0.9Sr0.1Cu3-yZnyTi4-xBxO12 ceramics by modifying grain boundary response

Ca0.9Sr0.1Cu3-yZnyTi4-xBxO12 ceramics (0.01 ≤ x ≤ 0.07, y = 0 and 0.05) were prepared using the citrate precursor process and sintered at 1100 °C for 3 h. X-ray diffraction (XRD) has confirmed that CaCu3Ti4O12 ceramics with single phase can be prepared for a short-term sintering. The results of XRD and Raman reveals the existence of secondary phase as x = 0.07. The energy dispersive spectrometer confirms the presence of Cu-rich phase at grain boundary, which leads to a weakened dielectric properties. B3+ doping can speed the grain growth, whereas Zn2+ doping decreases grain size slightly and high dense microstructures were observed. The introduction of Zn2+ leads to an increase of grain boundary resistance, a decrease of dielectric loss and an enhancement of frequency stability of dielectric properties. Enhanced dielectric properties with dielectric constant of ~13410 and dielectric loss of ~0.038 were observed for the sample at x = 0.04 and y = 0.05. Moreover, the nonlinear electrical characteristics are enhanced with proper concentration of Sr, B and Zn additions. The present results indicate that the improved dielectric properties of doped CCTO ceramics are mainly attributed to the improved microstructure and the modified grain boundary response.

Electrical properties of SiC-AlN ceramics pressureless sintered under N2 atmosphere

SiC-AlN ceramics were pressureless sintered at 2150 °C under N2 atmosphere, while B4C and C were added to promote the sintering process. The microstructure, electrical and mechanical properties of the as-sintered ceramics prepared by different AlN addition are discussed. More AlN addition tends to lead a smaller grain size. As AlN contents go up, the varistor voltage of the samples increases sharply from 17.304v·mm−1 to more than 100 v·mm−1 because of the improvement of grain boundary resistance. Correspondingly, the reasons for the increase of grain boundary resistance are: (1) the improvement of carrier compensation increases the Schottky barrier height and width; (2) more grain boundaries increase the number of Schottky barriers. In addition, the electrical properties of the same components sintered under N2 and Ar have been compared, that the varistor voltage of the same component SiC-AlN ceramics sintered under N2 are much higher than those under Ar (about 2 orders of magnitude). With the increase of AlN contents, the mechanical properties remain unchanged except the little reduction of Vickers hardness.

Enhanced energy storage properties of La-doped Pb0.99Nb0.02(Zr0.85Sn0.13Ti0.02)0.98O3 antiferroelectric ceramics

Pb0.99Nb0.02(Zr0.85Sn0.13Ti0.02)0.98O3-x mol% La (PNZST-xLa, x = 0, 0.005, 0.01, and 0.02) antiferroelectric ceramics with orthorhombic perovskite structure were synthesized by solid-state reaction methods and the effect of La content on the phase stability and energy storage properties of PNZST-xLa was investigated. The introduction of La can enhance the stability of antiferroelectric phase and broaden the dielectric peak. Moreover, La doping leads to an increase of grain boundary resistance. La-doped PNZST ceramics show larger recoverable energy density and higher energy efficiency than un-doped PNZST ceramic due to the increased switching electric field and polarization as the La doping. Meanwhile, the temperature- and electric field-dependent energy storage properties were studied. The energy storage density increases with increasing electric field but declines with increasing temperature.

Ultrahigh energy storage performance and fast charge-discharge capability in Dy- modified SrTiO3 linear ceramics with high optical transmissivity by defect and interface engineering

The excellent energy storage and pulse charge-discharge performance ceramics with high temperature stability and optical transmissivity are competitive for the development of electronic devices. In this work, comprehensive improved performances are simultaneously realized in DyxSr1-xTiO3 (DST) ceramics through defect and interface engineering. Meanwhile, increased high insulation grain boundary and reduced carrier mobility promote the increase of grain boundary resistance, and the increase of grain resistance primarily originates from the fact that DyTi' can easily attract oxygen vacancy, forming defect dipoles and restraining the movement of oxygen vacancies. Additionally, the relative density of ceramics is increased by sintering in O2 and doping Dy ions. Hence, x = 0.008 ceramics exhibit high coverable energy storage density of 4.00 J/cm3, high energy storage efficiency of 89.49%, excellent frequency (1Hz-1 kHz) and temperature stability (20-120 °C) and transmittance of >60% are achieved at 510 kV/cm at 0.2 mm. Furthermore, x = 0.008 ceramics possess the prominent current density of 420.1 A/cm2 and the prominent power density of 19.2 MW/cm3. Meanwhile, the short discharge rate of 20 ns and excellent stability of temperature (20-120 °C) are also achieved, suggesting that it is one candidate with strong potential for the application of lead-free high power capacitors.

Effect of Sn4+ doping on the dielectric and nonlinear J–E properties of CaCu3Ti4.1O12 ceramics with a slight titanium excess for X9R capacitors

Sn4+ doped CaCu3Ti4.1−xSnxO12 (x = 0.00, 0.05, and 0.10) ceramics were prepared using a one-step polymer pyrolysis method. Variation of Δe′ < ± 15% over a temperature range of − 60 to 210 °C, very low tanδ ~ 0.009–0.012 and giant-e′ ~ 6685–14,194 at 30 °C and 1 kHz were achieved in ceramics with x = 0.05 and 0.10 sintered at 1080 °C for 7 h. Furthermore, tanδ values of less than 0.03 and Δe′ < ± 10% over wide temperatures range of − 60 to 150 °C and − 60 to 200 °C were obtained in each of the ceramics. Both ceramics are promising candidate materials for X9R capacitor and X-P capacitor applications. The increase of grain boundary resistance (Rgb) with increasing Sn4+ content in the presence of a TiO2 phase are suggested to play an important role in extending Δe′ < ± 15% and tanδ < 0.05 over a wider temperature range.

A Strategy to Mitigate Grain Boundary Blocking in Nanocrystalline Zirconia

A major challenge in the application of nanostructured electrolytes in solid oxide electrochemical cells is grain boundary blocking originated from unsatisfied atomic bonding and coordination. The resulting increase in grain boundary resistivity works against the expected benefits from the enhanced ion exchange rates enabled by the extensive interfacial network in nanocrystalline materials. This study addresses this challenge by demonstrating that a reduction in the grain boundary excess energies increases the net ionic conductivity as directly measured by impedance electrical spectroscopy in nanocrystalline yttria-stabilized zirconia. The reduced grain boundary energy was designed by doping the system with lanthanum, leading to local excess energy reduction due to segregation of La to boundaries as observed by scanning transmission electron microscopy-based energy-dispersive spectroscopy. The results suggest rare-earth ions with favorable grain boundary segregation enthalpy can smooth out the energy land...

Dielectric Properties of NaCu3Ti3Nb1–xSbxO12 Ceramics

ABSTRACTIn order to investigate the influence of Sb doping on the dielectric properties of NaCu3Ti3NbO12 ceramics, a series of NaCu3Ti3Nb1–xSbxO12 ceramics were prepared by conventional solid-state reaction technique. Their crystalline structure, microstructure, dielectric properties and complex impedance were systematically investigated. All these ceramics show giant permittivity phenomenon, and their low-frequency dielectric loss decrease significantly but permittivity remains large with increased Sb doping. Impedance spectroscopic analysis reveals that NaCu3Ti3Nb1–xSbxO12 ceramics are composed of insulating grain boundaries and semiconducting grains, and their resistance of grain boundary increases with increased Sb doping. According to internal barrier layer capacitance effect, the decrease of low-frequency dielectric loss in NaCu3Ti3Nb1–xSbxO12 ceramics with increased Sb doping should be caused by the increase of grain boundary resistance.

Very high thermal stability with excellent dielectric, and non-ohmics properties of Mg-doped CaCu3Ti4.2O12 ceramics

In this work, the nominal CaCu3−xMgxTi4.2O12 (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ) < 0.009–0.014 and giant dielectric constant (e′) ∼ 1.1 × 104–1.8 × 104 with excellent temperature coefficient (Δe′) less than ± 15% in a temperature range of − 60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg2+ dopants due to the increase of grain boundary resistance (Rgb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg2+ dopants in the structure. In addition, CaCu3−xMgxTi4.2O12 ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (Eb) due to Mg2+doping. The high values of e′ (14012), α (13.64) and Eb (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu2.90Mg0.10Ti4.2O12 ceramic sintered at 1100 °C for 8 h.

Effect of MgO addition and grain size on the electrical properties of Ce0.9Gd0.1O1.95 electrolyte for IT-SOFCs

The aim of this study is to investigate the effect of grain size on the electrical properties of Ce0.9Gd0.1O1.95-x mol% MgO (GDC-xMgO) and to evaluate them as electrolytes for use in intermediate-temperature solid oxide fuel cells (IT-SOFCs). For this purpose, GDC-xMgO (x = 0–15) electrolytes were synthesized by the glycine-nitrate process and sintered at different temperatures. Impedance spectroscopy measurements revealed that for each composition, the grain-boundary resistivity decreased with decreasing grain size for the samples with grain size of >0.4 μm. Much too small grain sizes (0.2 < dg < 0.3 μm) produced an increase in grain-boundary resistivity. The addition of MgO could weaken the influence of grain sizes on the grain-boundary resistivity. The interfacial polarization resistances could be decreased by adding MgO to GDC. The GDC-1MgO sample sintered at 1200 °C exhibited the highest total conductivity of 8.11 × 10−2 S cm−1 at 800 °C. The maximum power density of the GDC-1MgO-based cell was 0.73 W cm−2 at 800 °C, which was much higher than that of the GDC-based cell. The results indicated that the GDC-1MgO was a potential electrolyte for IT-SOFCs.

Sintering behavior and electrochemical performances of nano-sized gadolinium-doped ceria via ammonium carbonate assisted co-precipitation for solid oxide fuel cells

Ultra-fine Gd-doped ceria (GDC) powders were synthesized via co-precipitation using ammonium carbonate as the precipitant. The crystallite size of the resultant GDC powders was measured as ∼33 nm. The dilatometry test of the powder compacts and the relative density measurement of sintered pellets with various sintering temperatures revealed the synthesized nano-GDC powders had superior sinterability compared to commercial GDC powders (e.g., 96% vs 78% in relative density at 1300 °C, respectively). Based on the total conductivity measurement of the co-precipitated GDC via electrochemical impedance spectroscopy, we found there was an optimum sintering temperature range (1300–1400 °C) to achieve both high density and high conductivity due to significant increase in grain boundary resistance at higher temperature (1500 °C). Moreover, the nano-sized and highly sinterable co-precipitated GDC effectively enhanced oxygen reduction reaction at the La0.6Sr0.4Co0.2Fe0.8O3−δ/GDC composite cathode due to increase in active reaction sites as well as enhanced phase connectivity in 3D-bulk at lower sintering temperatures.

Influence of microstructure on local intra- and intergranular deformations during creep of a nickel-based superalloy at 700 °C

Several microstructural parameters of the NR6 nickel-based superalloy were varied by applying four heat treatment procedures. Tensile creep tests were performed in air at 700°C and 700MPa on specimens exhibiting different grain sizes, strengthening γ′ precipitate sizes and distributions and grain boundary morphologies. Flat creep specimens were instrumented thanks to a dedicated microextensometry technique to analyze the local intra- and intergranular deformations after tensile creep under vacuum at 700°C. Tertiary γ′ precipitate dissolution, grain boundary serration and larger grain size reduce grain boundary sliding contribution to overall strain. These effects are attributed to the promotion of Orowan by-passing instead of shearing of the γ′ strengthening particles by matrix dislocations, increase of grain boundary resistance or decrease of grain boundary fraction. Relationships between local deformations and macroscopic creep behavior have been evidenced.

Investigation on CuCa3Ti4O12 Modified BiFeO3‐Based Perovskite Ceramics

(BiFeO3)1−x–(CuCa3Ti4O12)x (x = 0.00, 0.10 and 0.20) ceramics had been prepared via the mixed route. The crystal structure transformation of BiFeO3 (BFO) from rhombohedral to pseudotetragonal phase was induced by 20 mol% CuCa3Ti4O12 (CCTO). Impedance measurements suggested the increase in grain boundary resistance, and CCTO addition could block the conduction path and stabilize the motion of defects. The dielectric constant and the loss tangent of BFO as a function of frequency were found to be incremental on increasing CCTO contents. The enhancement of magnetization would be attributed to the effective suppression of the spiral spin structure and the structure transformation.

The Dielectric Characteristics of Sr and Mg Doped CCTO Ceramics

Two kinds ceramics of pure CaCu3Ti4O12 (CCTO) and Sr/Mg doped (Ca0.25Cu0.75)0.5Sr0.5TiO3 + xMgO (x=0.01, 0.03, 0.05, 0.1, denoted as CCST-M-1, CCST-M-3, CCST-M-5, CCST-M-10, respectively) were prepared using the traditional solid phase reaction method. The dielectric properties were measured by HP 4194A Impedance/Gain-Phase Analyzer with the frequency range from 100 Hz to 1MHz. The temperature dependence of dielectric constant and loss tangent were measured for different frequencies. The variation relation of the critical temperature with the frequency was fitted theoretically which is in agreement with the Arrhenius law for pure CCTO. According to a variable power law to describe the paraelectric dielectric constant of ferroelectrics with diffuse phase transitions, the theoretical fitting was carried out for doped samples, and it was suggested that all doped samples exhibited the Debye-like relaxation. Among the doped and pure CCTO samples, CCST-M-1 was of the lowest dielectric loss at the whole measurement frequency, and whose I–V response curve was nonlinear suggesting a non-ohmic contact. The complex-impedance analysis results showed that the reduction in dielectric loss of CCST-M-1 sample can be attributed to the increase of grain boundary resistance. It is expect that these results are helpful to promote the CCTO-related materials to practical applications.