Narrow Results

The phase formation and thermal-induced phase transformation are studied in BaTiO₃ nanoparticles. 2 h of heating a polymer precursor at 550°C in air formed a single phase BaTiO₃ of 15 nm average crystallite size D. The X-ray diffraction peaks are analyzed assuming a P_nma orthorhombic (o) crystal structure of lattice parameters a = 0.6435 nm, b = 0.5306 nm, and c = 0.8854 nm. The lattice volume V = 0.3023 nm³, with z = 4 formula units, yields a density ρ = 5.124 g/cm³. This is a new polymorph in comparison to well-known P_m3m tetragonal (t) structure, V = 0.0644 nm³ or ρ = 6.016 g/cm³ (z = 1). An o ↦ t transformation appears on heating at temperature as high as 650°C in air. A proposed model explains the transformation above a certain D value in terms of the Gibbs free energy. Unless heating above 750°C, the two phases coexist in a composite structure (D≤27 nm), with as much residual o-phase trace as ~28 vol%. As a function of temperature both the phases decrease in the V values up to 0.2975 and 0.0643 nm³ at 750°C respectively (0.0650 nm³ at 650°C). This is an important parameter for designing useful ferroelectric and other properties in a hybrid composite structure.

The aim of this study was to evaluate the damage modes of ceramic systems bonded to dentin under Hertzian indentation. Single-cycle Hertzian contact test over 150–850 N load range was applied randomly to 210 ceramic–dentin bilayer disc specimens of zirconia or IPS Empress II -1 mm, -1.5 mm and of feldspathic porcelain -1 mm, -1.5 mm, -2 mm. Optical microscopy was employed for the identification of quasiplastic mode and radial cracks. Finite element analysis was used to analyze the stress distribution. Our results showed that the degree of damage in both modes evolved progressively and the origin changed with contact load. Stress location and value were consistent with the mechanical test results. It was concluded that microstructure and thickness of the material have a significant effect on the damage modes of ceramic layer systems.

Ceramics with the composition Pb_1-xK_2x-3yM_yNb₂O₆ (PKMN) with x = 0.29, y = 0.145 and M = Gd³⁺, Y³⁺ were synthesized by the solid-state reaction route between the corresponding oxides and carbonates. The crystal structure was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric properties were measured from 35 to 595°C. Well-developed P–E (polarization–electric field) hysteresis loops were observed in the materials. Determining the piezoelectric constants, K_p = 20%, K_t = 49%, d₃₃ = 110, and quality factor, Q_m = 33, reveals that the material Y³⁺-modified PKN can be useful for transducer applications.

Polycrystalline sample of NaCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis exhibits the orthorhombic crystal structure of the compound at room temperature. Detailed dielectric studies of NaCa₂Nb₅O₁₅ over a wide range of temperature (31–500°C) and frequency (10²–10⁶ Hz) did not show any dielectric anomaly (or ferroelectric phase transition) as observed in other members of the tungsten bronze structural family. However, the low loss tangent and dielectric constant increase with increasing temperature. Complex impedance and modulus plots (at different temperature and frequency) show the existence of non-Debye type of relaxation process in the compound. Complex modulus spectrum shows only grain contribution in the compound. Electric modulus analysis suggests that a possible hopping mechanism is evident for electrical transport processes in the system. Studies of AC conductivity with frequency suggest that the material obeys Jonscher's universal power law.

In this paper we report samarium substituted Ba_0.80Pb_0.20Ti_0.90Zr_0.10O₃ (BPZT) ceramics. The material series with compositional formula Ba_0.80-xSm_xPb_0.20Ti_0.90Zr_0.10O₃ with x varying from 0 to 0.01 in the steps of 0.0025 was chosen for investigations. The material was synthesized by solid state reaction method. Reacted powders compacted in the form of circular discs were sintered at 1325°C. All the samples were subjected to X-ray analysis and found to be single phase. Dielectric behavior was studied as a function of frequency and temperature and Curie temperature (T_c) was determined. T_c was found to decrease with increasing x. The details are discussed and presented here.

The LiCo_3/5Fe_2/5VO₄ ceramics has been fabricated by solution-based chemical method. Frequency dependence of the dielectric constant (ε_r) at different temperatures exhibits a dispersive behavior at low frequencies. Temperature dependence of ε_r at different frequencies indicates the dielectric anomalies in ε_r at T_c (transition temperature) = 190°C, 223°C, 263°C and 283°C with (ε_r)_max ~ 5370, 1976, 690 and 429 for 1, 10, 50 and 100 kHz, respectively. Frequency dependence of tangent loss (tan δ) at different temperatures indicates the presence of dielectric relaxation in the material. The value of activation energy estimated from the Arrhenius plot of log(τ_d) with 10³/T is ~(0.396 ± 0.012) eV.

CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by the solid-state reaction route. Effect of sintering time was studied on the polarization (P) versus electric field (E) behavior. Unlike conventional ferroelectric hysteresis loop, PE hysteresis behavior in CCTO ceramics was observed to exhibit ferroelectric-like loop where polarization does not saturate but gives a maximum value. Remnant polarization and maximum polarization was observed to increase with sintering time. Current (I)–voltage (V) characteristics shows a nonlinear behavior making them useful for varistor applications. Coefficient of non-linearity (α) is also found to depend on sintering duration.

To meet the requirement of next-generation multilayer ceramic capacitors, the synthesis and characterization of Ba_0.985Bi_0.01TiO₃-based high-k dielectric compositions are reported. Solid solutions with a nominal composition of 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_1-xZr_xO₃ (x = 0.001, 0.005, 0.01, 0.02, 0.04, 0.06, 0.1) was synthesized by distillation method. Room-temperature X-ray diffraction patterns showed an increase and then a decrease in the tetragonality of Ba_0.985Bi_0.01TiO₃ after modifying with BaTi_1-xZr_xO₃. The decrement in tetragonality (c/a ratio) was accompanied by lowering of Curie temperature. 0.4Ba_0.985Bi_0.01TiO₃–0.6BaTi_0.995Zr_0.005O₃ was found to exhibit diffuse phase transition accompanied by an ultrahigh dielectric constant of 77,619, a loss tangent < 1 and a grain size < 1 μm.

In this paper, V₂O₅ added Li–Mn–Ti ferrites were prepared by the conventional double sintering ceramic technique having the compositional formula where "x" is the amount of V₂O₅ added and x = (0.0, 0.1, 0.2 and 0.3) wt.%. The samples were pre-sintered at 650°C for 2 h and then finally sintered at 950°C for 1 h. Single phase cubic spinel structures of the samples were confirmed by XRD studies. Various structural and electrical properties were studied and compared with those measured from sample of same composition but prepared with 0.5 wt.% of Bi₂O₃. This sample was pre-sintered at 850°C for 4 h and sintered at 1050°C for 4 h. Adding V₂O₅ in Li-ferrites was found to reduce the sintering temperature and obtained products with reduced porosity and crystallite size but with enhanced DC resistivity. From the studies of dielectric properties, it is found that V₂O₅ added ferrites have lower dielectric constant and dielectric loss. Temperature dependence of dielectric properties was also studied and temperature dependence of dielectric constant and dielectric loss were less significant in the V₂O₅ added Li-ferrites.

The influence of nickel doping on the electrical properties and dielectric relaxation in Zn${}_{1-x}$Ni${}_x$Fe₂O₄ (ZNFO, $0.2\le x\le 0.5$) ceramics has been investigated via the dielectric and complex impedance spectra measurements. According to the modified Curie–Weiss law, the diffusivity factor of the ZNFO ceramics from 1.69 to 2.02 with $x$ increasing from 0.2 to 0.5, respectively. Two relaxation peaks are observed in the nickel doped samples, by employing the modified Arrhenius equation, two activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. The Cole–Cole plots showed that the semicircular arcs which are nonideal Debye type, and the grain boundaries resistance increases with increasing Ni concentration.

Li₄Ti₅O${}_{12}$ ceramics with different amount of MoO₂ addition were densified at 850${}^{\circ }$C via a solid-state reaction route. Pure phases and dense crystal morphology were obtained. Our experimental results indicated that the ${\tau }_f$ value of the Li₄Ti₅O${}_{12}$ ceramic can be adjusted to near zero via adopting suitable amount of MoO₂ addition. Among all the modified Li₄Ti₅O${}_{12}$ specimens, the sample with 4 wt.% of MoO₂ addition (marked as LM4 in this paper) possessed good microwave dielectric properties: ${𝜀}_r=20.76$, $Q\times f=18308$ GHz (7.99 GHz), ${\tau }_f=(+)2.96$ ppm/${}^{\circ }$C. It is suggested that the MoO₂ modified Li₄Ti₅O${}_{12}$ ceramics are suitable candidates for LTCC applications in microwave devices.

The composite of $(1-x){\mathrm{\text{BaTiO}}}_3$–$(x){\mathrm{\text{Li}}}_{0.5}{\mathrm{\text{Fe}}}_{2.5}{\mathrm{\text{O}}}_4(x=0.00,0.05,0.10,0.15)$ was prepared by mixing lithium ferrite and barium titanate. The samples were sintered at 1150${}^{\circ }$C for optimum parameters at chemical reaction between ferrite–ferroelectric interfaces. The presence of ferroelectric nature was detected by X-ray diffraction (XRD) and homogenous coarseness nature was confirmed by scanning electron microscope (SEM). Dielectric measurement for the samples show the superimposition behavior of both magnetic and electric phases in the composite samples. This fact was further supported by magnetic behavior from vibrating sample magnetometer (VSM) and polarization from PE loops. Magnetic measurements show the increase in coercivity and saturation magnetization with increase in ferrite content. PE loops suggests that coercivity increases initially and then decreases for rise in ferrite content suggesting the trend of leaking factor in the samples.

B₂O₃–Bi₂O₃–SiO₂–ZnO (BBSZ) glass-modified Li₂(Mn${}_x$Ti${}_{1-x}$)O₃ ceramics were fabricated via a solid-state reaction route. Pure phase and dense crystal morphology were obtained at 900${}^{\circ }$C. Suitable amount of Mn${}^{4+}$-ion substitution could adjust the ${\tau }_f$ value of the Li₂(Mn${}_x$Ti${}_{1-x}$)O₃ system to near zero. Among all of the Li₂(Mn${}_x$Ti${}_{1-x}$)O₃ samples, the sample with x = 0.9 (marked as BL9 in this paper) possessed good microwave dielectric properties: ${𝜀}_r$ = 18, Q × f = 14,056 GHz (9.58 GHz) and ${\tau }_f$ = (+)2.43 ppm/${}^{\circ }$C. It is suggested that the Li₂(Mn${}_x$Ti${}_{1-x}$)O₃ ceramic with BBSZ glass is a suitable low-temperature co-fired ceramic (LTCC) candidate for microwave applications.

The materials’ consolidation, especially ceramics, is very important in advanced research development and industrial technologies. Science of sintering with all incoming novelties is the base of all these processes. A very important question in all of this is how to get the more precise structure parameters within the morphology of different ceramic materials. In that sense, the advanced procedure in collecting precise data in submicro-processes is also in direction of advanced miniaturization. Our research, based on different electrophysical parameters, like relative capacitance, breakdown voltage, and $\mathrm{\text{tg}}\delta$, has been used in neural networks and graph theory successful applications. We extended furthermore our neural network back propagation (BP) on sintering parameters’ data. Prognosed mapping we can succeed if we use the coefficients, implemented by the training procedure. In this paper, we continue to apply the novelty from the previous research, where the error is calculated as a difference between the designed and actual network output. So, the weight coefficients contribute in error generation. We used the experimental data of sintered materials’ density, measured and calculated in the bulk, and developed possibility to calculate the materials’ density inside of consolidated structures. The BP procedure here is like a tool to come down between the layers, with much more precise materials’ density, in the points on morphology, which are interesting for different microstructure developments and applications. We practically replaced the errors’ network by density values, from ceramic consolidation. Our neural networks’ application novelty is successfully applied within the experimental ceramic material density $\rho =5.4\times 10^3$ [kg/m³], confirming the direction way to implement this procedure in other density cases. There are many different mathematical tools or tools from the field of artificial intelligence that can be used in such or similar applications. We choose to use artificial neural networks because of their simplicity and their self-improvement process, through BP error control. All of this contributes to the great improvement in the whole research and science of sintering technology, which is important for collecting more efficient and faster results.

In this work, an attempt is made for improving the piezoelectric properties of a lead-free (Na${}_{0.5}$K${}_{0.485}$Li${}_{0.015})$(Nb${}_{0.98}$V${}_{0.02})$O₃ ceramic system by doping manganese in it. The Rietveld analysis of XRD micrographs of the ceramics indicates the samples crystallizing into 99.86% of orthorhombic phase and very small traces of tetragonal phase around room temperature. The Curie temperature ($T_c$) is hardly affected by the incorporation of Mn${}^{4+}$ into the system. At the manganese concentration of 0.02wt.%, the ceramic system attains the peak values in its density, dielectric constant at room temperature (${\epsilon }_{\text{RT}}$), planar electromechanical coefficient ($k_p)$, piezoelectric coefficient ($d_{33}$), and remnant polarization ($P_r$). The optimum piezoelectric properties of $k_p=43$% and $d_{33}=193$ pC/N are observed for this composition. The study reveals that the modification of (Na${}_{0.5}$K${}_{0.485}$Li${}_{0.015}$) (Nb${}_{0.98}$V${}_{0.02})$O₃ with an appropriate quantity of Mn${}^{4+}$ can produce the desired changes in the crystallographic properties and densification so as to eventually improve its piezoelectric properties.