Lead-free Perovskite Compounds Research Articles

(K0.5Bi0.5)ZrO3 (KBZ) lead-free perovskite compound: Structural study and physical properties

The structural study of (K0.5Bi0.5)ZrO3 compound (KBZ) evidenced a cubic ABO3 perovskite structure (space group: No 221 Pm3‾m, lattice parameter: a = 0.4157 nm). Above room temperature, the lattice parameter increases linearly, with linear expansion coefficient α = 6.4 × 10−6 K−1. No phase transition or decomposition occurs up to 1273 K (1000 °C). Below room temperature, small anomalies in Differential Scanning Calorimetry (DSC) and dielectric losses (tan(δ)) remain structurally unexplained and will need further investigation. Furthermore, KBZ appears as difficult to sinter. Although the A-site of the ABO3 perovskite lattice is occupied by two ions of different valences (K+/Bi3+, mixed occupancy), we did not detect relaxor behaviour in KBZ dielectric properties. However, electrostriction was observed at room temperature. This property, combined to the limited thermal evolution of the relative permittivity indicate that KBZ may be an interesting material, provided that the sintering can be improved.

Molecular Orbital Calculation of Lead-Free Perovskite Compounds for Efficient Use of Alkaline and Alkaline Earth Metals

The effective ionic charges of lead-free perovskite dielectric complex compounds were investigated with molecular orbital calculation. The base model was a double perovskite cluster that consisted of octahedral oxygen cages with a transition metal ion of titanium, niobium, or zirconium located at each of their centers, and alkali and/or alkaline earth metal ions located at the body center, corners, edge centers, or face centers of the cluster. The results showed significant covalent bonds between the transition metals and the oxygens, and the alkali metals, especially sodium and oxygen. On the other hand, the alkaline earth metals have weak covalency. Calculation was also performed with the replacement of some of the oxygens with chlorine or fluorine; such replacement enhances the covalency of the transition metals. These trends provide good guidelines for the design properties of lead-free perovskite piezoelectrics based on ubiquitous sodium use.

Effects of Structural Factors on Piezoelectric Performance of Lead-free Perovskite Compounds

Three powders with compositions close to 0.98(Na0.50K0.45Li0.05)NbO3−0.02Ca(Zr0.5Ti0.5)O3 (NKLN−CZT) were synthesized using a malic acid complex solution method, and three solid solutions were then fabricated using a conventional solid-state reaction technique. The optimal substitutional Ta content and Zr/Ti ratio for NKLN−CZT were examined by measuring the piezoelectric properties. Based on the results, a 0.98(Na0.50K0.45Li0.05)(Nb0.98Ta0.02)O3−0.02Ca(Zr0.4Ti0.6)O3 solid solution was fabricated to clarify the synergistic effect when the optimal values for both these parameters were used. The resulting material was found to exhibit the maximum longitudinal piezoelectric coefficient of 240 pC/N and radial electromechanical coupling factor of 41%. On the basis of these results and those for the average and local structure obtained using high-energy X-ray diffraction, this compound has potential as a high-Curie-temperature, high-performance, lead-free piezoelectric material.

Structural, thermal, electrical and magnetic features of a new lead-free electronic material: (SbLi)1/2(Fe2/3W1/3)O3

Low electric and magnetic moment features are the main drawbacks that restrict the practical utilities of bismuth ferrite. Successfully, we have substituted Li+ and W6+ in Sb3+ and Fe3+ sites to eliminate further confinements of bismuth ferrite (referred as BFO/BiFeO3). A new lead-free perovskite compound of (SbLi)1/2(Fe2/3W1/3)O3 (symbolized as SLFWO) has been produced through ceramic processing (high temperature) route. The calcination temperature of said compound is confirmed from the thermogravimetric analysis. The structural, microstructural, magnetic and electrical (dielectric constant/loss, impedance, modulus, conductivity) features of the said material have been studied over an extensive range of frequency (100 Hz-1 MHz) and temperature (RT-400 °C). The finding of reflection indices and crystal parameters approve the development of polycrystalline nature with orthorhombic symmetry of the compound. The impedance analysis confirms the existence of non-Debye type relaxation trend. The frequency-temperature dependence of ac-conductivity studies proves the nature and conduction mechanism in the compound. At specific peak frequency, the modulus spectrum movements of the charge carrier vary from wide array to narrow array. The peak frequencies increase with temperature signifying the thermally activated relaxation process. The value of leakage current rises with the temperature that established the NTCR trend of the compound. The observed values of remanent magnetization, saturation magnetization and coercivity of SLFWO are 0.5647 emu/g, 0.04953 emu/g, and 104.242 Oe respectively.

Synthesis and Characterization of Lead-Free (CH3)3SSnI3 1-D Perovskite

We report on the preparation, crystal structure and spectral properties of the trimethylsulfonium tin triiodide perovskite, (CH3)3SSnI3. The air-sensitive lead-free perovskite compound is prepared by reacting the (CH3)3SI and SnI2 solid precursors in evacuated silica tubes at 100°C. According to powder x-ray diffraction and Rietveld analysis, (CH3)3SSnI3 crystallizes at room temperature in hexagonal symmetry and forms a 1D network of face-sharing [SnI6] octahedra along the c axis. UV–Vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 2.85 eV accompanied by a weak luminescence signal. Multi-temperature Raman spectroscopy reveals a fully reversible structural phase transition just below 0°C related to the reduction of the unit cell symmetry. Comparison with the widely studied Cs-, CH3NH3- and (NH2)2CH-based 3D-perovskites that are commonly used in third generation solar cells confirms the higher stability of (CH3)3SSnI3. This is attributed to the beneficial role of the bulky trimethylsulfonium group in the ASnI3 structure.

Structure and properties of (Na0.5Bi0.5)ZrO3 (NBZ) lead-free perovskite compound

The structure of NBZ was studied by neutron diffraction. NBZ is monoclinic, (SG #11 P21/m) am = 5.696(8) Å, bm = 8.166(9) Å, cm = 5.790(4) Å and βm = 89.97(4)°. Being centrosymmetric, NBZ is neither piezoelectric nor ferroelectric. No phase transition was evidenced between 100 K and 923 K. NBZ presents a relaxor behavior below room temperature attributed to the mixed occupancy of the A-site by both Na+ and Bi3+ ions. The relative permittivity of NBZ appears noticeably stable (for 1 kHz −2.9% at −55 °C/218 K and +5.3% at 85 °C/358 K compared to the 25 °C/298 K value). NBZ appears thus as promising for the elaboration of capacitors requiring high thermal stability.

Lead-free hybrid perovskites for photovoltaics.

This review covers the state-of-the-art in organo–inorganic lead-free hybrid perovskites (HPs) and applications of these exciting materials as light harvesters in photovoltaic systems. Special emphasis is placed on the influence of the spatial organization of HP materials both on the micro- and nanometer scale on the performance and stability of perovskite-based solar light converters. This review also discusses HP materials produced by isovalent lead(II) substitution with Sn2+ and other metal(II) ions, perovskite materials formed on the basis of M3+ cations (Sb3+, Bi3+) as well as on combinations of M+/M3+ ions aliovalent to 2Pb2+ (Ag+/Bi3+, Ag+/Sb3+, etc.). The survey is concluded with an outlook highlighting the most promising strategies for future progress of photovoltaic systems based on lead-free perovskite compounds.

Synthesis of Lead-Free Perovskite Films by Combinatorial Evaporation: Fast Processes for Screening Different Precursor Combinations

We demonstrate an evaporation-based combinatorial approach for fast screening of precursor combinations for the synthesis of novel perovskite materials. Nine material combinations can be explored simultaneously, which enabled us to synthesize nine different lead-free perovskite compounds. The structural properties (morphology, crystal structure) and optical properties (UV–vis absorption spectra, photoluminescence) of the prepared materials were investigated. Among these materials, several Sn-based and Pd-based perovskites exhibit strong absorption in the visible spectral range and thus may be of interest for photovoltaic applications. In addition, butyl ammonium tin iodide exhibits bright red emission, and it is of interest for potential light emitting applications.

High-Temperature Monoclinic Cc Phase with Reduced c/a Ratio in Bi-based Perovskite Compound Bi2ZnTi1–xMnxO6

Monoclinic phases with Cm, Pm, and Cc space groups are indispensable to understand the high performance of electromechanical properties at the morphotropic phase boundary (MPB) of lead-based perovskite oxides Pb(ZrxTi1-x)O3 (PZT), [Pb(Mg1/3Nb2/3)O3]1-x-(PbTiO3)x (PMN-PT), and [Pb(Zn1/3Nb2/3)O3]1-x-(PbTiO3)x (PZN-PT). Here, a nearly single monoclinic phase with space group Cc was observed in the Bi-based lead-free perovskite compound Bi2ZnTi1-xMnxO6 at x = 0.4. This phase was the same as the low-temperature phase of the MPB composition of PZT but existed at a much higher temperature. Despite the reduced pseudo c/a ratio of 1.065, which is the same as that of PbTiO3 at room temperature, ionic model calculation based on the Rietveld refinement data indicated the polarization of Bi2ZnTi0.6Mn0.4O6 is 95.8 μC/cm(2). The tilting and significant anisotropic distortion of the octahedron were found to cause the c/a ratio to reduce. Accordingly, the effective piezoelectric constant d33 of Bi2ZnTi0.6Mn0.4O6 thin film was found to be 12 pm/V.

Diffuse Phase Transition in Ba(SnxTi1-x) Ceramics and Thin Films

Due to the need to limit the use of Pb in electrical products, dielectric materials based on lead-free perovskite compounds with relaxor behavior are being actively developed. In this study, we carried out an investigation on the perovskite material Ba(SnxTi1-x)O3, whose B-site ions comprise elements from different periodic table groups but have the same valence state of 4+. We fabr icated and evaluated ceramics, single layer solid solution (SS) thin films, and order-controlled superlattice (SL) thin films. The shape of the dielectric anomaly in these materials was demonstrated and the value of parameter γ, calculated from the Curie-Weiss law, was found to be 1.71 for ceramics, 1.86 for SS films and 1.90 for 33% ordered SL films. In addition, the influence of the order-disorder transition on diffuse phase transition (DPT) was clarified.