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Ceramic samples of (Bi${}_{1-x}$Pb_x)NbO₄ ($x=0$, 0.025, 0.05, 0.10, 0.15, 0.20) with 0.75wt.% V₂O₅ addition sintered at 920${}^{\circ }$C, 940${}^{\circ }$C and 960${}^{\circ }$C are investigated. Pb is selected as a substitute for Bi${}^{3+}$ in BiNbO₄ ceramics as it exists in two stable valence states of $+$2 and $+$4 and the average valency matches to that of Bi${}^{3+}$. The average Shannon radius (for octahedral coordination) of Pb${}^{2+}$ (1.19Å) and Pb${}^{4+}$(0.775Å) cations is 0.9825Å, which is similar to that of Bi${}^{3+}$ ion (1.03Å). The dense ($>94$%) polycrystalline (Bi${}_{1-x}$Pb_x)NbO₄ samples fabricated mostly reveal orthorhombic (Pnna) phase ($\alpha$-BiNbO₄, Sp. Gp. 52) by powder XRD. Presence of satellite Pb₂Nb₂O₇ phase, the amount of which is increasing with increase in Pb content, is also noticed. The microwave dielectric constant (${\epsilon }_r^{\prime }$) values of the niobates are found to increase from 42 to 71, whereas the quality factor (Q_u.f) values are found to decrease from 5400 to 550 GHz with increasing substitution of Pb. The compositions so synthesized are important as hardly there are any microwave dielectric ceramics available with $45<{\epsilon }_r^{\prime }<75$.

The solid solutions of the (1-x)Na${}_{0.5}$Bi${}_{0.5}$TiO₃-xNa${}_{0.5}$K${}_{0.5}$NbO₃ system were produced by the conventional ceramic technology using mechanical activation of the synthesized product. It was found that in the (1-x)Na${}_{0.5}$Bi${}_{0.5}$TiO₃-xNa${}_{0.5}$K${}_{0.5}$NbO₃ system at room temperature, a number of morphotropic phase transitions occur: rhombohedral → cubic → tetragonal → monoclinic phases. The introduction of a small amount of Na${}_{0.5}$K${}_{0.5}$NbO₃ leads to an increase in the temperature stability of the dielectric properties of ceramics. A change in the relaxor properties of the solid solutions of the (1-x)Na${}_{0.5}$Bi${}_{0.5}$TiO₃-xNa${}_{0.5}$K${}_{0.5}$NbO₃ system was shown. The increase in energy density and energy efficiency was found at additive 10mol.% of Na${}_{0.5}$K${}_{0.5}$NbO₃.

In this paper, we investigated the influence of rare earth ($\mathrm{\text{RE}}=\mathrm{\text{La}}$ and Gd) doped Ba${}_{0.9575}$RE${}_{0.04}$Ca${}_{0.0025}$Ti${}_{0.80685}$ Mn${}_{0.002475}$Nb${}_{0.002475}$Zr${}_{0.1782}$O₃ (BCTMNZ) ceramics were fabricated by using a conventional solid-state reaction method. The doping effects of La and Gd on the structural and magnetic properties were studied. The structural pattern of the ceramic samples were investigated by X-ray diffraction and the results indicated that both samples shows an orthorhombic structure with pure phase. Strain and crystalline size values for Gd and La doped were 0.31–0.33% and $0.154$–$0.181\mu$m, respectively. The room temperature hysteresis loops were obtained by using a vibrating sample magnetometer. La doped ceramic showed the higher value of magnetization i.e., $0.369\mu$B/f.u. as compared to Gd doped BLTMNZ ceramics.

(${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ($x=$ 0.00–0.30) ceramics were successfully prepared via the conventional solid-state method. X-ray powder diffraction confirmed the lattice constant gradually decreases with increasing Y${{}^3}^{+}$ content. SEM images displayed Y${{}^3}^{+}$ substitution for Bi${{}^3}^{+}$ gave rise to the large abnormal grains, and the size of abnormal grains became larger with the increase of Y${{}^3}^{+}$ substitution. (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics presented the relatively high dielectric constant of 7400 with the dielectric loss of 0.055 when $x=$ 0.20. The analysis of complex impedance suggested the grains are semiconductive and the grain boundaries are insulating. For pure ${\text{Bi}}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics, the appearance of additional low-frequency peaks in electrical modulus indicated the grain boundaries are heterogeneous. The investigation of modulus peaks fitting with Arrhenius formula implied that the low-frequency permittivity for all (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics was ascribed to the Maxwell–Wagner relaxation at grain boundaries. In addition, a set of clear dielectric peaks above ${200}^{\circ }$C associated with Maxwell–Wagner relaxation can be found for all (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics in the temperature dependence of dielectric constant. This set of clear dielectric peaks showed a tendency to shift to higher temperatures with the increase of Y${{}^3}^{+}$ substitution. Meanwhile, a tiny dielectric anomaly at room temperature was found in Y-doped ${\text{Bi}}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics.

Dense (${\text{Na}}_{0.5}$${\text{K}}_{0.5})$NbO₃ lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO₂, $\sim$${\text{10}}^{-12}$ atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added (${\text{Na}}_{0.5}$${\text{K}}_{0.5})$NbO₃ ceramics sintered in air and the low pO₂-sintered pure (${\text{Na}}_{0.5}$${\text{K}}_{0.5})$NbO₃ ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant $d_{33}$ is 125 pC/N, and the converse piezoelectric constant $d_{33}$* is 186 pm/V. The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03, respectively. Under the measured electric field of 70 kV/cm, the remanent polarization is 25.9 $\mu$C/cm² and the coercive field is 13.9 kV/cm. Furthermore, if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO₂ atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes.

Thin films of polycrystalline (Ba${{}_{1-}}_x$${\text{Sr}}_x)$TiO₃ ($x$ = 0.2 and 0.3) with Perovskite structure were prepared by a dip and dry technique on a platinum-coated silicon substrate. The good quality thin films with uniform microstructure and thickness were successfully produced by dip-coating techniques annealed at 730${}^{\circ }$C for 1 h. The resulting thin film shows a well-developed dense polycrystalline structure with more uniform grain size distribution. The BST thin films were characterized for their structural, Raman spectroscopy, morphological properties, and complex impedance properties. The dielectric constant-frequency curve showed the good dielectric constant and loss dielectric loss with low-frequency dispersion. The BST 0.3 thin film reveals that the dielectric constant and dielectric loss at a frequency of 1 kHz were 578 and 0.02, respectively. The obtained results on dielectric properties can be analyzed in terms of the Maxwell–Wagner model.

Lead free 0.94(Bi${}_{0.5}$Na${}_{0.5})$TiO₃–0.06BaTiO₃ ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by $\sim$3–4 orders of magnitude and an associated activation energy of 1.57eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities ($\rho \sim 10^3\mathrm{\Omega }$-cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi${}_{0.5}$Na${}_{0.5})$TiO₃. Long term annealing studies were also conducted at 800${}^{\circ }$C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi${}_{0.5}$Na${}_{0.5})$TiO₃–0.06BaTiO₃ ceramics are very sensitive to Bi/Na stoichiometry.

Polycrystalline ${\text{Na}}_{0.9}$${\text{Ba}}_{0.1}$${\text{Nb}}_{0.9}$(${\text{Sn}}_{0.5}$${\text{Ti}}_{0.5}{)}_{0.1}$O₃ is prepared by the solid-state reaction technique. The formation of single-phase material was confirmed by an X-ray diffraction study and it was found to be a tetragonal phase at room temperature. Nyquist plots ($Z^{\prime \prime }$ versus $Z^{\prime })$ show that the conductivity behavior is accurately represented by an equivalent circuit model which consists of a parallel combination of bulk resistance and constant phase elements (CPE). The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity ${\sigma }_{dc}$ follows the Arrhenius relation. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (KWW), $\phi (t)$ = exp($-(t$/$\tau {)}^{\beta })$ function and the value of the stretched exponent ($\beta )$ is found to be almost independent of temperature. The near value of activation energies obtained from the analyses of modulus and conductivity data confirms that the transport is through an ion hopping mechanism dominated by the motion of the (${\text{O}}^{2-})$ ions in the structure of the investigated material.

Ceramic samples of the ($1-x$)BaTiO₃⋅xPbFe${}_{2/3}$W${}_{1/3}$O₃, $0\le x\le 1$ (($1-x$)BT⋅xPFW) system were synthesized by solid-state reactions method. The samples were characterized by X-ray diffraction (XRD) and dielectric studies, as well as by the measurements of the thermally stimulated depolarization currents (TSDC). It was found that the predominant phase in the samples is presented by the (Ba${}_{1-x}$Pb_x)(Ti${}_{1-x}$Fe${}_{2x/3}$W${}_{x/3}$)O₃ solid solutions with a perovskite structure, herewith the samples with $0\le x<0.25$ are practically single-phase, and with $0.25\le x<1$ contain the impurity phase BaWO₄ (up to 15 mass.% at $x=0.60$–0.90). Information has been obtained about the changes in the structural and dielectric characteristics of the solid solutions with the change of their composition. It is established that the solid solutions crystal lattice symmetry at 296 K changes from tetragonal at $x\le 0.04$ to cubic at $x\ge 0.05$. An increase in the PFW content in solid solutions causes a gradual change in their properties from ferroelectric at $0\le x<0.10$ to relaxor ferroelectric at $0.10\le x\le 0.25$, and then to properties similar to those of the dipole glass with weak or zero correlation between dipoles at $0.25<x\lesssim 0.90$. The addition of BT to PFW leads to rather quick degradation of the relaxor ferroelectric properties of PFW in the region $x=0.9$–1.0.

Using the conventional solid-state reaction method, 0.5wt.% of MnO₂-, NiO-, Cr₂O₃-, Fe₂O₃- and Co₂O₃-added 0.94${\text{Na}}_{0.5}$${\text{Bi}}_{0.5}$TiO₃ (NBT)–0.06BaTiO₃ (BT) ceramics were prepared. The perovskite nature of the prepared ceramics was analyzed by powder XRD and the surface morphology was studied by means of SEM. The dielectric analysis was carried out from room temperature to $350^{\circ }$C at various frequencies and the diffusive transition at the dielectric maxima confirmed the relaxor nature of the ceramics. Creation of oxygen vacancies by the possible substitution of ferromagnetic impurities decreased the dielectric constant and piezoelectric constant ($d_{33})$. The co-existence of ferromagnetism and the ferroelectricity was observed in the Mn, Ni, Co and Cr-added NBT–BT ceramics. The magnetic force microscopy (MFM) analysis was carried out to study the ferromagnetic domains in the prepared ceramic.

Multiferroic ${\mathrm{BiFeO}}_3$ (BFO) and Y, Zr codoped BFO $\left({\mathrm{Bi}}_{1-x}{\mathrm{Y}}_x{\mathrm{Fe}}_{0.95}{\mathrm{Zr}}_{0.05}{\mathrm{O}}_3\right)$ ceramics were prepared and the influence of codoping on the crystal structure and magnetic properties were investigated in this work. Confirmed by the evolution of X-ray diffraction and Raman modes, the codoping has changed the crystal structure from rhombohedral to tetragonal in bulk BFO ceramics. The enhancement of magnetic behaviors is demonstrated by the damage of space-modulated spiral spin structure, and it can be attributed to the crystal structure change and size effects. Meanwhile, Raman spectra from 300 to 800 K demonstrates that lower frequency phonon modes show rapid softening near the Neel temperature.

Aluminium phosphate (AlPO₄)-Magnesium fluoride (MgF₂) composite has been prepared through solid state ceramic route. The formation of composite has been confirmed by X-ray diffraction studies. The variation in ε_r and tanδ of the composite with frequency in the range (1K Hz – 3 MHz) has been studied. The AlPO₄-MgF₂ has a small temperature dependence of ε_r. The composite shows low relative permittivity of 3 and low dielectric loss (tanδ = 7×10⁻³) at 5.85 GHz.

The paper presents the results of a comprehensive study of the thermophysical properties (thermal conductivity, thermal diffusivity, heat capacity) of high-temperature multiferroic BiFeO₃ modified with rare-earth elements (REEs) (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu). The regularities of the formation of the mentioned characteristics were established. The assumptions about the nature of the observed phenomena were suggested.

A lead-free relaxor ferroelectric, Sr${}_{0.15}$Ba${}_{0.85}$Bi₂Nb₂O₉, was synthesized via solid-state reaction and the temperature-dependence of the heat capacity was measured in a wide temperature range. The dielectric permittivity was also measured between 500Hz and 5MHz in the same temperature range. No anomaly has been detected in the heat capacity curve for the whole temperature range covered in the present experiments, while broad peaks have been observed in the dielectric permittivity with high frequency dispersion. A typical relaxor behavior has been observed from the dielectric analysis. The Debye’s temperature has showed a minimum value near the freezing temperature. The results are discussed considering the spin-glass model and the high frequency dispersion, which has been observed for the studied relaxor system.

The solid solutions of ($1-x$) LaFeO₃–$x$BaTiO₃ (0.0$\le x\le$0.25) have been synthesized successfully by the conventional solid-state reaction method. Room temperature (RT) X-ray diffraction studies reveal the stabilization of orthorhombic phase with Pbnm space group. Complete solubility in the perovskite series was demonstrated up to $x=0.25$. The dielectric permittivity shows colossal dielectric constant (CDC) at RT. The doping of BaTiO₃ in LaFeO₃ exhibit pronounced CDC up to a composition $x=0.15$, further it starts to decrease. The frequency-dependent dielectric loss exhibits polaronic conduction, which can attribute to presence of multiple valence of iron. The relaxation frequency and polaronic conduction mechanism was shifted towards RT as function of $x$. Moreover, large magnetic moment with weak ferromagnetic behavior is observed in doped LaFeO₃ solid solution, which might be the destruction of spin cycloid structure due to insertion of Ti in Fe–O–Fe network of LaFeO₃.

In this paper, we present impedance spectroscopy of Sodium Bismuth Titanate-based materials belonging to (1-x)Na_1/2Bi_1/2TiO_3-xBaTiO₃(x = 0.04) (NBT–BT) system. NBT–BT ceramics are prepared by high temperature solid-state reaction method. X-ray diffraction technique showed single-phase polycrystalline sample with an ABO₃ perovskite structure. Dielectric behavior and the impedance relaxation were investigated in a wide range of temperature (room temperature (RT) –500°C) and frequency (1 kHz–1 MHz). A broad dielectric constant peak was observed over a wide temperature range around the phase transition temperature. The complex impedance plot exhibited one impedance semicircle identified over the frequency range of 1 kHz–1 MHz, which is explained by the grain effect of the bulk. The centers of the impedance semicircles lie below the real axis, which indicates that the impedance response is a Cole–Cole type relaxation.

Low-temperature co-fired ceramics (LTCC) applied in millimeter/microwave and terahertz frequencies (5G/6G) have attracted a lot of attention recently. In this study, MgO-based dielectric ceramics were successfully sintered at 950°C with the sintering aids: x wt.% of LiF fluoride ($x=2$, 4, 6, 8, 10) and 0.5wt.% of BBSZ (Bi₂O₃–B₂O₃–SiO₂–ZnO) glass. BBSZ glass was introduced as another sintering aid to facilitate the sintering and densification. Crystalline structure and micro-morphology were investigated and analyzed. Dielectric properties (${\epsilon }_r$, $Q\times f$, ${\tau }_f$) at millimeter/microwave and terahertz wave frequencies were also studied. The ionic characteristics of Mg–O bond ($f_i$), the lattice energy (U) and the bond energy (E) were calculated and analyzed. It is suggested that the optimal $x=4$, where ${\epsilon }_r=10.5$, $Q\times f=120,000$GHz (@12GHz) and ${\tau }_f=-26$ppm/°C at millimeter/microwave range. When the frequency was up to terahertz (1.0THz), the ${\epsilon }_r$ values were 8.8–9.35 and the tan$\delta$ were $5.6\times 10^{-3}$–$8.7\times 10^{-3}$. The experimental results indicated that the low-temperature sintered MgO-based ceramics have potential for millimeter/microwave and terahertz communication applications.

Solid solutions of the composition Ba${{}_{1-}{}_x{}_{-}}_y$(Mg, Ln)${}_x$${\text{Sr}}_y$TiO₃ ($x$ = 0.01; 0.025; 0.04; $y$ = 0.20; 0.50; 0.80; Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb) were prepared by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. The influence of rare-earth elements on the microstructure of the prepared ceramic samples was investigated. It was found that regardless of the type of modifiers introduced, the grain landscape of the studied solid solutions with different amounts of SrTiO₃ is refined (in the initial system, the average grain size, $\bar{d}$, at $x$ = 0.20 is 6 $\mu$m; at $x$ = 0.50 is 4 $\mu$m; at $x$ = 0.80 is 18 $\mu$m) to crystallite sizes not exceeding (2-3) $\mu$m, and compacted. The using of mechanical activation procedures leads to an even greater decrease in the size and an increase in the density of ceramics. The increasing in the concentration of modifiers in each group (within the considered range of dopant variation) against the background of such a fine-grained structure has little effect on the dynamics of changes in $\bar{d}$. It is concluded that it is advisable to use the data obtained in the development of functional materials based on BST/(Mg, Ln) and devices with the participation of these compositions.

The paper discusses the features of the effect of modification with lithium carbonate on the dielectric dispersion of lead ferroniobate ceramics. The modifier has been previously shown to change the ways of the recrystallization sintering and therefore reduce the sintering temperature of the ceramics, increase their average grain size, and improve their dielectric and piezoelectric properties. In this study, the emphasis is placed on the analysis of the diffusion effects of the ferroelectric phase transition upon such modification considered from the standpoint of the chemical specifics of the modifier and its location in the structure of the parent compound.

Phase diagrams were constructed (at room temperature), the dielectric, piezoelectric, elastic and reversible properties of the Ge-modified $x$PbTiO₃–$y$PbZrO₃–$z$${\text{PbNb}}_{2∕3}$${\text{Mg}}_{1∕3}$O₃ multicomponent system ceramics were studied. The data obtained are compared with the results of studies of solid solutions of basic binary systems, as well as with the results obtained previously for other sections of the system under consideration. A significant increase in the width of the morphotropic region, diffusion of the concentration dependences of the electrophysical characteristics, and an increase in stability under the influence of constant bias fields in the solid solutions of the studied system were established.