Macroscopic and Microscopic Structures of Cesium Lead Iodide Perovskite from Atomistic Simulations

A first‐principles‐based effective Hamiltonian is developed and employed to investigate finite‐temperature structural properties of a prototype of perovskite halides, that is CsPbI₃. Such simulations, when using first‐principles‐extracted coefficients, successfully reproduce the existence of an orthorhombic Pnma state and its iodine octahedral tilting angles around room temperature. However, they also yield a direct transformation from Pnma to cubic $Pm\overline{3}m$ upon heating, unlike measurements that reported the occurrence of an intermediate long‐range‐tilted tetragonal P4/mbm phase in‐between the orthorhombic and cubic phases. Such disagreement, which may cast some doubts about the extent to which first‐principle methods can be trusted to mimic hybrid perovskites, can be resolved by “only” changing one short‐range tilting parameter in the whole set of effective Hamiltonian coefficients. In such a case, some reasonable values of this specific parameter result in the predictions that i) the intermediate P4/mbm state originates from fluctuations over many different tilted states; and ii) the cubic $Pm\overline{3}m$ phase is highly locally distorted and develops strong transverse antiphase correlation between first‐nearest neighbor iodine octahedral tiltings, before undergoing a phase transition to P4/mbm under cooling.     

Effect of hot pressing on processing and properties of BBN ceramics

BBN (BaBi₂Nb₂O₉) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators.     

Dielectric, Ferroelectric and Piezoelectric Studies of PMN Modified PLZT Ceramics

Dielectric, ferroelectric and piezoelectric properties of xPb(Mg_1/3Nb_2/3)O₃-(1-x)(Pb_0.988 La_0.012)(Zr_0.535Ti_0.465)O₃ ceramic system synthesized through columbite precursor method are investigated. X-ray diffraction patterns of ceramics indicated pseudocubic phase formation with pyrochlore phase. Grain growth (4.47 μ m) and apparent density (7.68 gm/cm³) enhanced remarkably in 0.8PMN-0.2PLZT composition, respectively. Increasing PMN content remarkably increased both room temperature dielectric permittivity (ε_RT = 2316) and dielectric maximum (ε_Tc = 24747) in 0.6PMN-0.4PLZT composition, respectively. PMN substitution in PLZT system enhanced the ferroelectric remanent (P_r = 28.4 μ C/cm²) and spontaneous (P_s = 31.2 μ C/cm²) polarization while coercive field (E_c) continuously decreased in xPMN-(1-x)PLZT system. PMN modification in PLZT system influenced piezoelectric properties (d₃₃, k_p and k_t) throughout the PMN-PLZT system.     

掺杂铁电纳米粉的液晶的电光特性

铁电纳米粒子悬浮在向列相液晶母体中，增强介电各向异性，而且对施加的电场信号敏感。本文也展示了纳米粒子对所述复合材料可实现的总的相变的作用。这种方法也许可应用于设计新型显示材料。     

Structural properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 relaxor ferroelectric thin films on SrRuO3 conducting oxides

Coating of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO₃ (SRO) metallic oxide electrodes on SrTiO₃ (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.     

Experimental Evaluation of the Acceptor-States Compensation in Positive-Temperature-Coefficient-Type Barium Titanate

Experimental evidence shows that the acceptor-state levels in Sb-doped positive-temperature-coefficient-type BaTiO₃ are compensated up to a critical acceptor-state density. Using the slope of the natural logarithm of the resistivity with respect to 1/ T , instead of maximum resistivity as a measure for the acceptor-state density, it is possible to estimate this critical value. The value obtained (4.2 × 10¹⁷ m⁻²) is believed to be the first reported estimate based on experimental data. It is in good agreement with the estimate of 6 × 10¹⁷ m⁻² (first reported by Jonker) obtained from the spontaneous polarization of BaTiO₃. This shows that the ferroelectric behavior of BaTiO₃ is indeed a feasible explanation for the low resistivity below the Curie point, as proposed by Jonker.     

Thin-Layer Dielectrics in the Pb[(Mg1/3Nb2/3)1-xTix]O3 System

Thin layers of Pb[(Mg_1/3Nb_2/3)_{1– x} Ti _x ]O₃ (PMNT) were prepared by spin casting alkoxide-based solutions on platinized Si. The effects of additives, heat treatment, and composition ( x = 0 to 0.9) on perovskite phase development, ceramic microstructure, and dielectric properties are reported. Depending upon the processing conditions, ceramic thin layers could be formed in a nonferroelectric pyrochlore phase (A₂B₂O₆) or in a ferroelectric perovskite phase (ABO₃). The dimensions of the pyrochlore and perovskite units cells were related and increased with Mg and Nb contents. To minmize pyrochlore formation, the most effective processing method involved rapid heat treatment between successive solution depositions. Phase development and microstructure were also affected by solution additives. Additions of benzoic acid were found to affect the structure in solution and the later organic pyrolysis behavior from thin layers. The effect of composition on the dielectric and ferroelectric properties is also reported.     

Systematic study of structure and piezoelectric properties of Pb(Ni1/3Nb2/3)O3-PbTiO3 by in situ synchrotron diffraction

Lead-based ferroelectric materials are extensively employed in industrial applications and everyday life due to their excellent ferroelectric and piezoelectric performance. Pb(Ni_1/3Nb_2/3)O₃-PbTiO₃ (PNN-PT) is a typical binary relaxor ferroelectric system, whose refined structure and piezoelectric properties have not been systematically investigated. In this study, evolution of electric field-based crystal structure and variation of ferroelectric, piezoelectric, as well as dielectric properties with composition and temperature of (1 − x)PNN-xPT (0.32 ≤ x ≤ 0.36) ceramics were studied in full detail. The optimal performance is obtained at 0.66PNN-0.34PT with maximum piezoelectric coefficient d₃₃ of 560 pC/N and large dielectric constant of 28 684. In situ high-energy synchrotron diffraction was employed to determine structural origins of enhanced properties of 0.66PNN-0.34PT. Interestingly, crystal structure of poled 0.66PNN-0.34PT ceramic is determined to be single monoclinic phase. Furthermore, both its lattice parameters and volume variation present butterfly shape under electric field. It is demonstrated that macroscopic strain of 0.66PNN-0.34PT stems mainly from intrinsic structure. The present study provides evidence for the relationship between microstructure and macroscopic properties, which is beneficial to the design of new materials with piezoelectric properties.     

Hydrostatic-pressure-induced depolarization of (Pb1-1.5xLax)(Zr0.80Ti0.20)O3 ferroelectric ceramics

Pulse power energy conversion materials with ultrafast discharge processes and ultrahigh power densities have been widely used in the defense, energy, medical, and mining fields. The pressure-driven depolarization in ferroelectric materials is significant and accounts for the discharge processes. In this study, we focus on pressure-induced depolarization in (Pb_1-1.5xLa_x)(Zr_0.80Ti_0.20)O₃ (PLZT) (x = 0-0.07) ceramics, and their corresponding phase structure, dielectric properties, ferroelectric properties, and thermal depolarization performances. Although a satisfactory pulse power energy conversion performance has been achieved in Pb(Zr_0.95Ti_0.05)O₃ materials, poor temperature stability negatively influences their application. The static charge densities of PLZT (x = 0.04, 0.06) decreased from 29.11 μC/cm² and 31.53 μC/cm² to 19.76 μC/cm² and 6.56 μC/cm² under 400 MPa hydrostatic pressure, respectively, which is attributed to a pressure-driven ferroelectric-antiferroelectric phase structural transition. In particular, the temperature stability of PLZT (x = 0.06) materials is up to 87°C. This study may guide the further development pulse power energy conversion devices.     

PMN-PNN-PT单晶的固相法生长研究

采用两步法和埋入PMN-PT单晶为模板的等离子放电烧结（SPS）技术制备出了致密的单一钙钛矿相的PMN-PNN-PT陶瓷，随后在1200℃下退火100h来诱导晶体的生长。实验结果表明，PMN-PNN-PT单晶〈111〉方向的生长速度明显快于〈001〉方向，而〈111〉方向生长的晶体形状为V字形，这是由钙钛矿结构的生长机理决定的，钙钛矿结构晶体的生长是通过〈001〉方向的层状生长来实现的。