Mechanisms responsible for enhancing low-temperature oxidation resistance of nonstoichiometric (Zr,Ti)C

A series of (Zr,Ti)C_x (x = 0.7–1.0) samples were fabricated by a modified spark plasma sintering apparatus to investigate the effects of carbon concentration and Ti substitutions on the oxidation behavior. Crushed powders of (Zr,Ti)C_x were oxidized in lab air (N₂–20-vol.% O₂) from room temperature to 900°C. The results indicated that Zr_0.8Ti_0.2C_0.8, with a nominal carbon concentration x = 0.8, displayed good oxidation resistance, which was attributed to the formation of dense t-(Zr,Ti)O₂ oxide solid solution. During the oxidation of (Zr,Ti)C_x, Ti substitutions for Zr enhanced the outward diffusion of carbon, enabling a uniform carbon layer and a Zr–Ti–C–O layer on the surface of carbides. The formed carbon layer improved the oxidation resistance of (Zr,Ti)C_x below 550°C, where carbon is relatively oxidation resistant. Increasing the Ti concentration was found to enhance the oxidation resistance of (Zr,Ti)C_x with an increased oxidation onset temperature (672 ± 2°C for Zr_0.8Ti_0.2C_0.8).     

Densification,microstructures, and mechanical properties of (Zr,Ti)(C,N) ceramics fabricated by spark plasma sintering

Dense (Zr, Ti) (C, N) ceramics were fabricated by spark plasma sintering (SPS) at 1900–2000 °C using ZrC, TiCN and ZrH₂ powders as raw materials. A single Zr-rich (Zr, Ti)(C, N) solid solution was formed in Zr_0.95Ti_0.05C_0.975N_0.025 and Zr_0.80Ti_0.20C_0.90N_0.10 ceramics (nominal composition). A Ti-rich solid solution appears in Zr_0.50Ti_0.50C_0.75N_0.25 ceramics. The coaddition of TiCN and ZrH₂ promoted the densification of (Zr, Ti) (C, N) ceramics by forming solid solutions and carbon vacancies, which could reduce critical resolved shear stress (CRSS) and promote carbon and metal atom diffusion. ZrC-45 mol% TiCN-10 mol% ZrH₂ (raw powder composition) possesses good comprehensive mechanical properties (Vickers hardness of 24.5 ± 0.9 GPa, flexural strength of 503 ± 51 MPa, and fracture toughness of 4.3 ± 0.2 MPa·m^1/2), which reach or exceed most ZrC-based (Zr, Ti) C and (Zr, Ti) (C, N) ceramics in previous reports.     

Microstructural,structural and dielectric properties of Er3+-modified BaTi0.85Zr0.15O3 ceramics

The (micro)structural and electrical properties of undoped and Er³⁺-doped BaTi_0.85Zr_0.15O₃ ceramics were studied in this work for both nominal Ba²⁺ and Ti⁴⁺ substitution formulations. The ceramics were produced from solid-state reaction and sintered at 1400 °C for 3 h. For those materials prepared following the donor-type nominal Ba_1?xEr_x(Ti_0.85Zr_0.15)O₃ composition, especially, Er³⁺ however showed a preferential substitution for the (Ti,Zr)⁴⁺ lattice sites. This allowed synthesis of a finally acceptor-like, highly resistive Ba(Ti,Zr,Er)O_3?δ-like system, with a solubility limit below but close to 3 cat.% Er³⁺. The overall phase development is discussed in terms of the amphoteric nature of Er³⁺, and appears to mainly or, at least, partially also involve a minimization of stress effects from the ion size mismatch between the dopant and host cations. Further results presented here include a comparative analysis of the behavior of the materials’ grain size, electrical properties and nature of the ferroelectric-to-paraelectric phase transition upon variation of the formulation and Er³⁺ content.     

High‐Energy Density Dielectrics and Capacitors for Elevated Temperatures: Ca(Zr,Ti)O3

The Ca(Zr_1?xTi_x)O₃ (CZT) solid solution system is a linear dielectric that is of interest for high‐temperature power capacitor applications. This dielectric was synthesized by conventional solid‐state processes and prototyped into single‐layer CZT capacitors, which were fabricated with interdigitated electrodes cofired between dielectric layers ~10‐μm thick. The dielectric properties of these capacitors were extensively investigated as a function of Zr/Ti ratio on the CaZrO₃ side of the solid solution. The electrostatic energy density and breakdown strength of the CZT capacitors were investigated by measuring polarization–electric field curves as a function of temperature from room temperature to 250°C. The Ca(Zr_0.80Ti_0.20)O₃ capacitors show high electrostatic energy density of 4 J/cm³ at 250°C. Highly accelerated life testing (HALT) was also performed on these dielectrics, and we quantified the thermal stimulated depolarization current (TSDC) to access the major point defects in the CZT system.     

Phase Evolution and Microstructural Studies in CaZrTi2O7–Nd2Ti2O7 System

A series of compositions with general stoichiometry Ca_1?xZr_1?xNd_2xTi₂O₇ has been prepared by high‐temperature solid‐state reaction of component oxides and characterized by powder X‐ray diffraction and electron probe for microanalyses (EPMA). The phase fields in CaZrTi₂O₇–Nd₂Ti₂O₇ system and distribution of ions in different phases have been determined. Four different phase fields, namely monoclinic zirconolite, cubic perovskite, cubic pyrochlore, and monoclinic Nd₂Ti₂O₇ structure types are observed in this system. The 4M‐polytype of zirconolite structure is stabilized by substitution of Nd³⁺ ion. The addition of Nd³⁺ ions form a cubic perovskite structure‐type phase and thus observed in all the compositions with 0.05 ≤ x ≤ 0.80. Cubic pyrochlore structure‐type phase is observed as a coexisting phase in the nominal composition with 0.20 ≤ x ≤ 0.90. Only a subtle amounts of Ca²⁺ and Zr⁴⁺ are incorporated into the perovskite‐type Nd₂Ti₂O₇ structure. EPMA analyses on different coexisting phases revealed that the pyrochlore and perovskite phases have Nd³⁺‐rich compositions.     

Structural,optical, electrical and dielectric properties of (Sr1-xMgx)(Sn0.5Ti0.5)O3 (X=0.00, 0.25, 0.50, 0.75) ceramics via solid state route

We have prepared (Sr_1-xMg_x)(Sn_0.5Ti_0.5)O₃, (X = 0.00, 0.25, 0.50, 0.75) samples by the solid state reaction method and studied the structural, optical, electrical modulus and the other dielectric properties of the samples with respect to variation in frequencies (1 × 10⁹ to 2 × 10⁹ Hz) using Impedance Analyzer. This study suggests that the XRD patterns of the samples have shown that this possesses cubic perovskite structure in space group Pm-3m and scanning electron microscope was used to analyze the grain size distribution and porosity of the ceramic. The dielectric properties of these materials were strongly dependent upon on concentration X as well as amount of frequencies. The existence of metal oxygen bonds of Sr–Ti–O was verified by Fourier Transform Infra Red (FTIR) spectrum at 540 cm⁻¹. The highest PL intensity of 716.38 that exhibits the green emission (508.5 nm) was obtained for the composition of (Sr_0.25Mg_0.75)(Sn_0.5Ti_0.5)O₃. AC conductivity slowly decreases with increasing Mg substitution and also the sample (Sr_0.25Mg_0.75)(Sn_0.5Ti_0.5)O₃ having the lowest (constant) value of conductivity at 1 GHz–2GHz.     

The influence of mechanical activation on the structure and phase formation of an electro-thermal explosion in the Ti–Zr–C system

The Ti_xZr_1-xC solid solutions were synthesized by electro-thermal explosion under pressure in the (Ti + Zr + C) blends mechanically activated in hexane (MA-ETE). The effect of mechanical activation (MA) duration on reaction blend characteristics, ETE parameters, phase composition, and microstructure formation in solid solutions was investigated. At MA, the Ti + Zr blend deforms metal crystal lattices for 20 min, complete amorphization occurs for 40 min, and the carbide grains form a cubic structure for 90 min. The single-phase Zr_0.50Ti_0.50C solid solution with a grain size of 3–5 μm and a submicron composite with a grain size of 0.1–0.2 μm containing the Ti_0.86Zr_0.14C and Zr_0.74Ti_0.26C solid solutions were synthesized in a one-stage process for the first time without any additional thermotreatment. The influence of mechanical activation on diffusional mass transfer of reactants, structure, and phase formation is discussed.     

Site-selective substitution and resulting magnetism in arc-melted perovskite ATiO3-δ (A = Ca,Sr, Ba)

Magnetic properties in perovskite titanates ATiO_3-δ (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis was conducted by powder synchrotron X-ray diffraction with Rietveld refinements. Quantitative chemical element analysis was carried out by X-ray photoelectron spectroscopy. Magnetic measurements were conducted by vibrating sample magnetometer and X-ray magnetic circular dichroism (XMCD). The magnetic properties are found to be affected by impurities of 3d elements such as Fe, Co, and Ni. Depending on the composition and crystal structure, the occupation of the magnetic ions in perovskite titanates is selectively varied, which is interpreted to be the origin of the different magnetic behaviors in arc-melted perovskite titanates ATiO_3-δ (A = Ca, Sr, Ba). In addition, both formation of oxygen vacancies and the reduction of Ti⁴⁺ to Ti³⁺ during arc-melting also play a role as proven by XMCD. Nevertheless, preferential site occupation of magnetic impurities is dominant in the magnetic properties of arc-melted perovskite ATiO_3-δ (A = Ca, Sr, Ba).     

Chlorobenzene total oxidation over palladium supported on ZrO2, TiO2 nanostructured supports

Two series of supported Pd catalysts were synthesized on new mesoporous–macroporous supports (ZrO₂, TiO₂) labelled M (Zr and Ti). The deposition of palladium was carried out by wet impregnation on the calcined TiO₂ and ZrO₂ supports at 400 °C (Pd/Zr₄, Pd/Ti₄) and 600 °C (Pd/Zr₆, Pd/Ti₆) and followed by a calcination at 400 °C for 4 h. The pre-reduced Pd/MX catalysts were investigated for the chlorobenzene total oxidation and their catalytic properties where compared to those of a reference catalyst Pd/Ti-Ref (TiO₂ from Huntsman Tioxide recalcined at 500 °C) and of a palladium supported on the fresh mesoporous–macroporous TiO₂ (Pd/Ti). Based on the activity determined by T₅₀, the Pd/Ti and Pd/Ti₄ catalysts have been found to be more active than the reference one. Moreover activity decreased owing to the sequence: Pd/TiX  Pd/ZrX and in each series when the temperature of calcination of the support was raised. The overall results clearly showed that the activity was dependant on the nature of the support. The better activity of Pd/TiX compared to Pd/ZrX was likely due to a better reducibility of the TiO₂ support (Ti⁴⁺ into Ti³⁺) leading to an enhancement of the oxygen mobility. Production of polychlorinated benzenes PhCl_x (x = 2–6) and of Cl₂ was also observed. Nevertheless at 500 °C the selectivity in HCl was higher than 90% for the best catalysts.     

Preparation and tunability properties of Ba(ZrxTi1−x)O3 thin films grown by a sol–gel process

Ba(Zr_xTi_1−x)O₃ (BZT) thin films were deposited via sol–gel process on LaNiO₃, as buffer layer, and Pt-coated silicon substrates. The BZT films were perovskite phase and showed a (1 0 0) preferred orientation dependent upon zirconium content. The grain size decreased and the microstructure became dense with increasing zirconium content. The addition of Zr to the BaTiO₃ lattice decreased the grain size of the crystallized films. The temperature dependent dielectric constant revealed that the thin films have relaxor behavior and diffuse phase transition characteristics that depend on the substitution of Zr for Ti in BaTiO₃. The dependence of electrical properties on film thickness has been studied, with the emphasis placed on dielectric nonlinear characteristics. Ba(Zr_0.35Ti₆₅)O₃ thin films with weak temperature dependence of tunability in the temperature range from 0 to 130 °C could be attractive materials for situations in which precise control of temperature would be either impossible or too expensive.     

Iron and chromium doped perovskite (CaMO3 M = Ti,Zr) ceramic pigments,effect of mineralizer

Solid solutions Ca(D_xM_1?x)O₃ (M = Ti, Zr and D = Fe,Cr), have been studied as ceramic pigment in conventional ceramic glazes using 0.5 mol/mol of NH₄Cl as flux agent by solid state reaction and by ammonia coprecipitation route. Ca(Cr_xTi_1?x)O₃ compositions obtained without addition of NH₄Cl as mineralizer, produce pink color in glazes at low x but CaCrO₄ crystallizes when x increases, producing undesired green colors. The crystallization of chromates can be avoided using NH₄Cl as mineralizer, giving a complete solid solution that produce pink color in glazes at low x and dark blue shades at high x. Coprecipitated sample produce blue colors at low x and at low temperature than ceramic sample (1000 °C instead 1200 °C for CE sample). Cr⁴⁺ ion acts as red chromophore, but at higher x values (blue samples) Cr³⁺ ion entrance affects the color. Ca(Fe_xTi_1?x)O₃ system crystallizes perovskite CaTiO₃ and pseudobrookite Fe₂TiO₅ together with rutile as residual crystalline phase, glazed samples change from a yellow to a pink color associated to the increase of pseudobrookite with firing temperature. Ca(Fe_xTi_1?x)O₃ and Ca(Cr_xZr_1?x)O₃ systems crystallize perovskite CaZrO₃ and zirconia (ZrO₂) in both monoclinic and cubic polymorphs, but iron or chromium oxides are not detected in the powders. Coprecipitated sample stabilises cubic form. The solid solution is not reached completely in these samples and is not stable in glazes.     

Dielectric properties and tunability of Ba(ZrxTi1−x)O3 ceramics under high DC electric field

Ba(Zr_xTi_1−x)O₃ (BZT) (x = 0.25, 0. 3, 0.35, 0.4) ceramics were prepared by the traditional ceramic processing and their structural, surface morphological, dielectric properties, tunable properties as well as the mechanism of their nonlinear dielectric constant under DC electric field were systemically examined. The Zr ions substitution of Ti ions has a strong effect on the dielectric properties and the grain sizes. The results show Ba(Zr_xTi_1−x)O₃ (x = 0.25, 0.3, 0.35) ceramics to be promising candidates for the DC electric field tunable materials for microwave electronics application, because they exhibit high tunability (27.6%, 26.3%, 19.4%, respectively) as the strength of electric field is up to 2 kV/mm, low dielectric loss (0.001–0.002, 0.001–0.002, 0.004–0.005, respectively) at 10 kHz at room temperature and low temperature coefficient of capacitance.     

Influence of Zr/Ti atomic ratio and seed layer on the magnetoelectric coupling of Pb(ZrxTi1−x)O3 film-on-CoFe2O4 bulk ceramic composites

Lead zirconate titanate Pb(Zr_xTi_1−x)O₃ films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe₂O₄ ceramics using a simple chemical solution deposition. All Pb(Zr_xTi_1−x)O₃ films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr_xTi_1−x)O₃ films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr_0.52Ti_0.48)O₃ films and CoFe₂O₄ substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr_0.52Ti_0.48)O₃ films with more or absolute (100)-texture and using conductive interfacial layer between two phases.     

Enhanced dielectric properties of La-doped 0.75BaTiO3-0.25Bi(Mg0.5Ti0.5)O3 ceramics for X9R-MLCC application

A series of 0.75Ba_(1?x)La_2x/3TiO₃-0.25Bi(Mg_0.5Ti_0.5)O₃ (x = 0–0.2) ceramics have been synthesized by doping La₂O₃ into 0.75BaTiO₃-0.25Bi(Mg_0.5Ti_0.5)O₃ (0.75BT-0.25BMT), and their structure and dielectric properties investigated. Upon characterizing the structural properties, the single-phase perovskite structure is identified for all the samples and the long-range order of 0.75BT-0.25BMT is verified to be further destroyed with the addition of La₂O₃. Moreover, it is found that the density of 0.75BT-0.25BMT can be improved by doping with La₂O₃, which also promotes the grain growth. Regarding the dielectric properties, the peak shifting effect induced by La³⁺ improves the permittivity-temperature stability of 0.75BT-0.25BMT remarkably by strengthening its relaxation behavior. Among all the samples, 0.75Ba_0.8La_0.4/3TiO₃-0.25Bi(Mg_0.5Ti_0.5)O₃ shows the most outstanding permittivity-temperature stability with ε_r = 572 ± 15% (compared with ε_r at 25 °C) over the temperature range ?70°C–238 °C at 1 kHz, which is notably better than that of 0.75BT-0.25BMT (?4°C–58 °C) and satisfies the specification of the X9R multilayer ceramic capacitor (MLCC). Our work provides one promising option for selecting an alternative dielectric material in terms of permittivity-temperature stability, which advances the development of the X9R MLCC.     

Phase decomposition of (Ti,Zr)(C,N) solid solutions prepared by spark plasma sintering

(Ti, Zr)(C, N) solid solutions with 10–90 mol% of ZrC were prepared by spark plasma sintering (SPS) using TiCN and ZrC powders as starting materials. The decomposition behavior of the (Ti, Zr)(C, N) solid solutions as a function of heat treatment temperature (1273–2173 K) was investigated. (Ti, Zr)(C, N) solid solutions with 20–80 mol% of ZrC were decomposed into TiCN-rich (Ti, Zr)(C, N) and ZrCN-rich (Zr, Ti)(C, N) phases when heat-treated in the temperature ranged from 1373 to 2173 K for 3.6 ks, respectively. After heat treatment, lamellar microstructure was formed with an orientation relationship of TiCN-rich (Ti, Zr)(C, N) {100} // ZrCN-rich (Zr, Ti)(C, N) {100}. The Vickers hardness and fracture toughness simultaneously increased with increasing heat-treatment temperature and showed the maximum values of 25.0 GPa and 2.5 MPa m^1/2, respectively, for Ti_0.5Zr_0.5C_0.75N_0.25 at the heat-treatment temperature of 1873 K.     

Phase transitional behavior and piezoelectric properties of BiYbO3–Pb(Ti0.5Zr0.5)O3–LiNbO3 ceramics

Perovskite (1 − x)(0.06BiYbO₃–0.94Pb(Ti_0.5Zr_0.5)O₃)–xLiNbO₃ (BYPTZ-LN) ceramics were synthesized by the conventional ceramic processing. The effect of LiNbO₃ on the microstructure and piezoelectric properties was investigated. The perovskite phase and the Yb₂Ti₂O₇ pyrochlore phase are coexisting in the BYPTZ-LN ceramics sintered at 1140 °C. The material with perovskite structure is tetragonal at x ≤ 0.04 and becomes single rhombohedral at x ≥ 0.08. A morphotropic phase boundary between rhombohedral and tetragonal phases is found in the composition range 0.04 ≤ x ≤ 0.08. Analogous to Pb(Zr,Ti)O₃, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d₃₃values reach 290–360 pC/N. Electromechanical coefficients k_p reach 0.38–0.55. The maximum values of d₃₃, k_p and P_r are obstained as x = 0.08, accompanying with the minimum values of Q_m and E_c. The Curie temperature T_c and the maximum value of dielectric constant decrease with increasing LiNbO₃ content. BYPTZ-LN ceramics with the high d₃₃ value and the high thermal-depoling temperatures of >320 °C are obtained.     

High Electric‐Induced Strain and Temperature‐Dependent Piezoelectric Properties of 0.75BF–0.25BZT Lead‐Free Ceramics

0.75BiFeO₃–0.25Ba(Zr_xTi_1?x) + 0.6 wt% MnO₂ (0.75BF–0.25BZT) ceramics with Mn addition were prepared by the solid‐state reaction method. The high‐field strain and high‐temperature piezoelectric properties of 0.75BF–0.25BZT ceramics were studied. Introduction of Zr in the solid solutions decreased the Curie temperature slightly, and improved the dielectric and piezoelectric properties obviously. The piezoelectric properties of 0.75BZT–0.25BT ceramics reached the maximum at Zr content of 10 mol%. The Curie temperature T_c, dielectric constant ε and loss tanδ (1 kHz), piezoelectric constant d₃₃, and planner electromechanical coupling factor k_p of 0.75BF–0.25BZT ceramics with 10 mol% Zr were 456°C, 650, 5%, 138 pC/N, and 0.30, respectively. The high‐field bipolar and unipolar strain under an electric field of 100 kV/cm reached up to 0.55% and 0.265%, respectively, which were comparable to those of BiScO₃–PbTiO₃ and “soft” PZT‐based ceramics. The typical “butterfly”‐shaped bipolar strain and frequency‐dependent peak‐to‐peak strain indicated that the large high‐field‐induced strain may be due to non‐180° domain switching. Rayleigh analysis reflected that the improved piezoelectric properties resulted from the enhanced extrinsic contribution by Zr doping. The unipolar strain of 0.75BF‐0.25BZT ceramics with 10 mol% Zr was almost linear from RT to 200°C. These results indicated that 0.75BF–0.25BZT ceramics were promising candidates for high‐temperature and lead‐free piezoelectric actuators.     

Improvement of dielectric loss of (Ba,Sr)(Ti,Zr)O3 ferroelectrics for tunable devices

(Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ (0.05 ≤ x ≤ 0.3) ferroelectric materials have cubic perovskite structure and show paraelectric properties at room temperature. Curie point shifted to a negative value as increasing Zr content in (Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ system. When Zr substituted 0.1 mol, the dielectric constant, dielectric loss, tunability, Curie point and FOM were 4500, 0.0005, 63%, −1.6 °C and 1260, respectively. This composition shows excellent microwave dielectric properties than those of (Ba_0.6Sr_0.4)TiO₃ ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters and frequency agile filters, etc.     

B-site acceptor doped AgNbO3 lead-free antiferroelectric ceramics: The role of dopant on microstructure and breakdown strength

B-site aliovalent modification of AgNbO₃ with a nominal composition of Ag(Nb_1-xM_x)O_3-x/2 (x = 0.01, M = Ti, Zr and Hf) was prepared. The effects of dopants on microstructure, dielectric, ferroelectric and conduction properties were investigated. The results indicate that the introduction of acceptor dopant does not lead to grain coarsening. Zr⁴⁺ and Hf⁴⁺ doping are beneficial to stabilize the antiferroelectric phase of AgNbO₃. Among all the samples, Ti⁴⁺ doped AgNbO₃ has the minimum resistivity while Hf⁴⁺ doped AgNbO₃ has the maximum resistivity, therefore, Hf⁴⁺ doped AgNbO₃ has high BDS. The XPS results indicate that the conduction behaviour is associated with the concentration of oxygen vacancies. This work hints that acceptor dopant is also effective on the microstructure control and chemical modification of AgNbO₃-based ceramics.     

Strong Effect of Oxygen Partial Pressure on Electrical Properties of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films

0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) epitaxial thin films were grown on SrRuO₃ (SRO) coated (001)‐oriented SrTiO₃ (STO) single crystal substrates by pulsed laser deposition under different oxygen partial pressures in the processing of deposition. The effects of oxygen partial pressure on structure, cation stoichiometry, surface morphology, leakage current behavior, ferroelectric, and piezoelectric properties were investigated. Both the lattice parameters and (Ba + Ca)/(Ti + Zr) cation ratio decrease with increasing oxygen partial pressure. The BCZT thin film with the ideal cation stoichiometry was obtained under 200 mTorr, giving rise to a remanent polarization P_r = 14.5 μC/cm² and effective piezoelectric coefficient d₃₃ = 96 ± 5 pm/V.