The effect of CuO and NiO doping on dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 lead-free ceramics

In the present work, lead-free piezoelectric ceramics (Na_0.5Bi_0.5)TiO₃ –xCuO–yNiO (for x = 0.0, 0.02, 0.04 and 0.06) have been prepared by a conventional solid-state reaction method. An investigation of CuO and NiO doping in bismuth sodium titanate (BNT) and a study of the structure, morphology, and dielectric and ferroelectric properties of the NBT–CuNi system have been conducted. Phase and microstructural analysis of the (Na_0.5Bi_0.5)TiO₃ (NBT) based ceramics has been carried out using X-ray diffraction and scanning electron microscopy (SEM) techniques. Field emission scanning electron microscopy (FE-SEM) images showed that inhibition of grain growth takes place with increasing Cu and Ni concentration. The results indicate that the co-doping of NiO and CuO is effective in improving the dielectric and ferroelectric properties of NBT ceramics. Temperature-dependent dielectric studies have also been carried out at room temperature to 400 °C at different frequencies. The NBT ceramics co-doped with x = 0.06 and y = 0.06 exhibited an excellent dielectric constant ?_r = 1514. The study suggests that there is enormous scope of application of such materials in the future for actuators, ultrasonic transducers and high-frequency piezoelectric devices.     

Structural and electrical properties of Na1/2La1/2TiO3 ceramics

Na_1/2La_1/2TiO₃ (NLT) ceramic was prepared by a high-temperature solid-state reaction technique. A preliminary structural analysis (XRD) suggested the formation of a single-phase orthorhombic structure. SEM micrograph of the material showed uniform grain distribution on the surface of the sample. The dielectric permittivity and the loss tangent of the sample were measured in a frequency range from 1 kHz to 1 MHz and a temperature range 28 °C to 525 °C. Electrical properties of the material were studied using an ac impedance spectroscopic technique. Detailed analysis of the impedance spectrum suggested that the electrical properties of the material are strongly temperature dependant. The Nyquist plots clearly showed the presence of both bulk and grain boundary effect in the compound. The activation energy was estimated to be 1.1 eV from the temperature variation of dc conductivity. The a.c. conductivity spectrum suggests a typical signature of ion conducting system. PACS 77.22.Ch; 77.22.Gm; 77.80.Bh; 77.22.Ej     

Structural and dielectric properties of phosphorous-doped PLZT ceramics

In the present work we have reported the unique effects of P₂O₅-doped PLZT ceramics with composition (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ +x wt% of P₂O₅ (wherex = 1, 3 and 5) prepared chemically by co-precipitation method. X-ray diffraction studies suggest that the prepared compound was very fine (10–25 nm), homogeneous and of rhombohedral symmetry. The apparent density of samples decreased with the P⁵⁺ additions. Studies of dielectric constant and dielectric loss as a function of frequency (10–1000 kHz) and temperature suggest that the compound undergoes diffuse type of phase transition without any sign of relaxor behaviour. With increasingx, dielectric constant was found to decrease appreciably, whereas Curie temperature (T_C) was found to increase     

Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li_1/4Dy_1/4W_1/2)O₃ have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.     

Structural,spectroscopic and dielectric properties of KVO3

Polycrystalline samples of KVO₃, a member of the pyroxene structural family have been synthesised with high-temperature solid-state reaction technique. Preliminary structural and spectroscopic and detailed dielectric properties have been studied in different conditions. No dielectric anomaly or hysteresis loop has been observed in a wide temperature range (30°C to 450°C). Basic structural and spectroscopic (IR and Raman) studies suggest that at room temperature, KVO₃ is centrosymmetric as reported earlier. This and other observations do not support the recent report of ferroelectric phase transition in the compound.     

Studies on structural and dielectric properties of Na1/2Dy1/2TiO3 ceramic

The polycrystalline sample of Na_1/2Dy_1/2TiO₃ ceramic was prepared by a standard high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of single-phase (with minor secondary phase) compound in the orthorhombic (distorted tetragonal) crystal system at room temperature. Study of surface morphology by scanning electron microscope exhibits uniform distribution of rectangular/cubical grains with less voids. The elemental composition of the prepared compound was confirmed by energy dispersive X-ray spectroscopy microanalysis. Detailed studies of dielectric properties exhibit a dielectric anomaly at 94 °C suggesting a possible ferroelectric–paraelectric phase transition in the compound. The activation energy (E_a), calculated from the temperature dependence of ac conductivity plot, was found to be small (∼0.1 eV) in low temperature and large (∼0.5 eV) in high temperature region.     

(Na1/2Bi1/2)Cu3Ti4O12陶瓷的微观结构和电学性质

利用固相反应法在不同烧结温度条件下制备了一系列(Na_1/2Bi_1/2)Cu₃Ti₄O₁₂(NBCTO)陶瓷样品,研究了它们的晶体结构、微观组织结构、介电性质和复阻抗及其随温度的变化. 实验发现NBCTO陶瓷所呈现出的电学性质与CaCu₃Ti₄O₁₂陶瓷相应的电学性质非常类似. 烧结温度为990℃至1060℃范围的NBCTO陶瓷样品室 关键词： 高介电材料 介电性质 复阻抗 内阻挡层电容     

Luminescence properties of K1/2Bi1/2TiO3:Pr3+ and Na1/2Bi1/2TiO3:Pr3+

The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects.     

铌酸钾钠基无铅压电陶瓷的X射线衍射与相变分析

分析了斜方相、四方相铌酸钾钠基无铅压电陶瓷材料的结构和X射线衍射图谱的特点. 对于铌酸钾钠基压电材料斜方相结构, 从构成晶胞的一个单斜原胞进行分析, 计算出X射线衍射谱上每个衍射角附近的衍射峰数目和相对强度. 提出了2θ在20°—60°范围内根据(1 0 2)衍射峰(52°附近)和(1 2 1)衍射峰(57°附近)劈裂的数目区分斜方和四方相的新方法. 对于多晶陶瓷粉末, 可以更简便的由22°(或45°)附近前后峰的相对高低来判断斜方、四方相. 关键词： 铌酸钾钠 无铅压电陶瓷 X射线衍射 相变     

Dielectric,ferroelectric and field-induced strain response of lead-free BaZrO3-modified Bi0.5Na0.5TiO3 ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaZrO₃ (BNT–BZ100x, with x = 0–0.10) were prepared using a conventional solid-state reaction method. The crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of BNT–BZ100x ceramics were studied as functions of different BZ content. X-ray diffraction patterns revealed that the BZ completely diffused in the BNT lattice in the studied composition range. An appropriate amount of BZ addition improved the dielectric, ferroelectric, and piezoelectric properties of BNT ceramics. The remanent polarization (P_r) and piezoelectric constant (d₃₃) increased from 22 μC/cm² and 60 pC/N for pure BNT to 30 μC/cm² and 112 pC/N for x = 0.040, respectively. In addition, electric field-induced strain was enhanced to its maximum value (S_max = 0.40%) with normalized strain (d*₃₃ = S_max/E_max = 500 pm/V) at an applied electric field of 8 kV/mm for x = 0.055. The enhanced strain can be attributed to the coexistence of ferroelectric and relaxor ferroelectric phases.     

(Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics with simultaneous addition of CeO2 and La2O3

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) with simultaneous addition of 0.5 mol% CeO₂ and 0.25, 0.5 and 0.75 mol% La₂O₃, respectively, was prepared by a conventional ceramic fabrication technique. An addition of 0.5 mol% CeO₂ together with 0.5 mol% La₂O₃ enhanced the piezoelectric and dielectric constant of BNBT-6 ceramics significantly. At room temperature, this composition exhibits a high piezoelectric constant (d₃₃=162×10^-12 C/N) and relatively low dielectric loss (cos=2.0%) at 1 kHz. X-ray diffraction pattern shows that the coexistence of tetragonal and rhombohedral phases in the BNBT-6 composition was not changed by adding CeO₂+La₂O₃, and they diffused into the BNBT lattice during sintering. SEM observation indicates that a small amount of CeO₂+La₂O₃ almost does not affect the microstructure. PACS 77.65.Bn; 77.84.Dy; 77.22.-d     

钇和镧掺杂氧化铝陶瓷的热导及其介电弛豫特性研究

采用氧化物固相反应法,制备出纯氧化铝陶瓷及其分别掺杂稀土元素钇和镧的陶瓷样品.测量了样品的结构、介电特性和热导性能;研究了烧结温度对掺杂不同稀土元素的陶瓷样品的性能的影响.X射线衍射结果表明1500℃烧结后陶瓷样品形成了单一的固溶体.而氧化铝的热导率达到8.60W/（m·K）,样品的介电性能稳定.我们发现掺杂Y³⁺和La³⁺的氧化铝陶瓷存在介电弛豫现象,并对该现象进行了机理分析.     

Structural and dielectric properties of La- and Ti-modified K0.5Na0.5NbO3 ceramics

We report the results of studies of rectifying behavior, positive magneoresistance (MR), the charge-transport mechanism and the effect of an electric field on a ZnO (n)/La_0.5Pr_0.2Sr_0.3MnO₃ (LPSMO) (p)/SrNb_0.002Ti_0.998O₃ (SNTO) (n) heterostructure comprising two p–n junctions fabricated using the pulsed laser deposition technique. The heterostructure exhibits rectifying behavior over a wide temperature and field range having hysteresis in I–V behavior (forward bias) due to the tunneling of charge carriers. It is also observed that, depending on the nature of the electric field bias to n-type ZnO and SNTO, the junction resistance becomes modified, which has been explained on the basis of spin injection in the heterostructure. The observation of unconventional positive MR at room temperature has been justified on the basis of interface effects and the reduction in barrier height obtained using fitting of the I–V data by a thermionic emission model.     

Effect of excess Bi2O3 on the electrical properties and microstructure of (Bi1/2Na1/2)TiO3 ceramics

(Bi_1/2Na_1/2)TiO₃ ceramics (BNT) with 0–6 mol% of excess Bi₂O₃ are prepared by conventional solid-state sintering. The electrical properties of the samples are examined. The addition of excess Bi₂O₃ reduces the leakage current of BNT ceramics significantly, thus facilitating the poling process, and improves their piezoelectric properties slightly for certain amounts of added Bi₂O₃. BNT ceramics have very high dielectric constants and dissipation factors at low frequency and high temperature due to their high conductivity. Adding excess Bi₂O₃ to BNT ceramics affects their dielectric behavior and phase transition temperatures. Grain growth is suppressed by adding Bi₂O₃ and no second phase is observed for BNT ceramics with up to 6 mol% of excess Bi₂O₃ added.     

溶胶-凝胶法制备的高压电常数（Bi0.5Na0.5）1－xBaxTiO3系无铅压电陶瓷

测量了使用溶胶-凝胶工艺制备的(Bi0.5Na0.5)1-xBaxTiO3(x=0.00，0.04，0.06，0.08,0.12)系陶瓷的介电、压电、铁电和热释电性能.由于使用了溶胶-凝胶工艺制备的粉料，因此所有样品的压电性能都得到了较大提高.其中(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷具有该系列最大的压电常数，d33=173×10-12C/N，与传统工艺相比，d33提高了近40%.同时，在一定范围内，随Ba含量的增加，材料的剩余极化Pr和矫顽场Ec逐渐减小，退极化温度逐渐降低.对于(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷，剩余极化和矫顽场分别为25μC/cm2和28kV/cm，退极化温度约为80℃. 关键词： 溶胶-凝胶 压电常数 剩余极化 矫顽场     

Effect of Mn doping on the acoustic and vibrational behaviors of lead-free piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 single crystals

The acoustic and vibrational properties of Mn-doped (Na_1/2Bi_1/2)TiO₃-xBaTiO₃ with x = 0.05 were investigated by using Brillouin and Raman spectroscopies and compared with those of undoped crystals. The mode frequency and the half width of the Brillouin doublet of the longitudinal acoustic mode showed more drastic changes near the dielectric maximum temperature compared to the broad and diffused changes of the undoped crystals, which indicates that Mn-doping induces polar domains larger than the typical polar nanoregions formed in undoped counterpart. The acoustic anomalies were most pronounced along the <100> direction suggesting that the polarization fluctuations are anisotropic and largest along this direction. Temperature dependence of Raman spectra showed that there are two characteristics temperatures where mode splitting occurs due to local symmetry changes. The high-temperature anomaly was associated with the changes in the acoustic properties, while the low-temperature mode splitting was related to the dielectric anomaly near depolarization temperature.     

Structural,thermal, electrical and magnetic properties of pure and 50% La doped BiFeO3 ceramics

Polycrystalline ceramic samples of pure and 50% La substituted BiFeO₃ have been prepared by standard solid state reaction method using high purity oxides and carbonates. The formation of the single phase compound as well as its chemical analysis has been checked by X-ray diffraction and energy dispersive X-ray microanalysis (EDAX) techniques. A better agreement between observed and calculated X-ray powder diffraction patterns was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group R3c. The lattice parameters in both the cases have been refined but the over-all structure remains the same. The microstructural studies have been carried out using scanning electron microscopy (SEM). Modulated differential scanning calorimetry (MDSC) has been used to detect the Neel/transition temperature in the compounds. The activation energies calculated from log σ vs 1/T curve are 0.81 eV and 1.13 eV respectively. Vibrating sample magnetometer (VSM) has been used to study the magnetic behaviour of the compounds. It has been observed that by 50% La substitution the insulating behaviour of the material has been improved and showing the antiferromagnetic to weak ferromagnetic behaviour.