Temperature-dependent dielectric properties of CsPb2Br5: a 2D inorganic halide perovskite

Observation of piezoelectricity in a lead-free Cs2AgBiBr6 perovskite: a new entrant in the energy harvesting arena

Halide perovskite materials have recently been recognised as powerful ferroelectric and piezoelectric materials with applications in the energy harvesting arena, but their experimental proof is very limited. We achieved strong intrinsic piezoelectricity in the lead-free inorganic double perovskite Cs2AgBiBr6 at room temperature and utilized it for mechanical energy harvesting, with a piezoelectric co-efficient (d33) of 12.7 pC N-1. Hysteresis loop and structural analyses offered further validation for the substantial ferroelectric features of the as-synthesised double perovskite. Density functional theory (DFT) calculations revealed the presence of anharmonic phonon soft modes in tetragonal Cs2AgBiBr6 due to dynamic instability, which resulted in piezoelectricity. Under an optimal pressure of ≈25 kPa, a Cs2AgBiBr6 thin film-based piezoelectric nanogenerator device delivered instantaneous output values of ≈45 V and ≈200 nA. The strain-sensitive responses of the device were also exemplified to identify specific body motions from the detected instantaneous output values. The energy obtained from the device is shown to be effective for capacitor charging and commercial light-emitting diode (LED) lighting. Our study provides significant insights into the dielectric behaviour of materials as well as piezo- and ferroelectric behaviours, which are crucial for the development of modern electronic and energy harvesting devices.

Crystal Structure and Spectroscopic Characterization of a New Hybrid Compound, (C12H17N2)2[CdBr4], for Energy Storage Applications

Organic-inorganic hybrid materials have recently found a vast variety of applications in the fields of energy storage and microelectronics due to their outstanding electric and dielectric characteristics, including high dielectric constant, low conductivity, and low dielectric loss. However, despite the promising properties of these materials, there remains a need to explore novel compounds with improved performance for practical applications. In this research paper, the focus is on addressing this scientific challenge by synthesizing and characterizing the new-centrosymmetric (C12H17N2)2[CdBr4] crystal. This compound offers potential advancements in energy storage technologies and microelectronics due to its unique structural and electronic properties. The chemical mentioned above crystallizes in the monoclinic system, and its protonated amine (C12H17N2)+ and isolated anion [CdBr4]2- are bound by C-H···π and N-H···Br hydrogen bonds to form its zero-dimensional structure. Through optical absorption analysis, the semiconductor nature of the material is verified, showcasing a band gap of around 2.9 eV. Furthermore, an in-depth examination of Nyquist plots reveals the material's electrical characteristics' sensitivity to frequency and temperature variations. By applying Jonscher's power law to analyze ac conductivity plots, it is observed that the variation in the exponent "s" accurately characterizes the conduction mechanism, aligning with CBH models. The compound exhibits low dielectric loss values and a high permittivity value (ε ∼ 105), making it a promising candidate for energy storage applications. By managing the scientific challenge of improving material performance for energy storage and microelectronics, this research contributes to advancing the field and opens avenues for further exploration and application of organic-inorganic hybrid materials.

Influence of potassium doping on the structural, conduction mechanism, and dielectric properties of CaFe2O4

The frequency and temperature-related dielectric relaxation and electrical conduction mechanisms in potassium-doped CaFe2O4 oxide ceramic were investigated in this study throughout a temperature range of 313-673 K. The synthesis of the KCaFe2O4 compound was accomplished through a solid-state reaction route. The X-ray diffraction pattern at room temperature confirmed that the ceramic KCaFe2O4 crystallizes in the orthorhombic system with the Pbnm space group. The EDX analysis proved the absence of external elements. The surface morphology of the samples was examined using scanning electron microscopy. The conduction mechanism, validated as CBH conduction, was examined using the temperature-dependent variation of Jonscher's power law exponent. Using Nyquist plots, we have effectively constructed a relevant equivalent circuit that encompasses the influences originating from both the grains and the grain boundaries. Furthermore, in KCaFe2O4, the induced dielectric relaxation from the non-Debye to Debye type model is demonstrated by the thermal analysis of M'' (ω) and -Z'' (ω) as a function of frequency.

Preferential perovskite surface-termination induced high piezoresponse in lead-free in situ fabricated Cs3Bi2Br9-PVDF nanocomposites promotes biomechanical energy harvesting

Lead-free halide perovskites have gained immense popularity in photovoltaic and energy harvesting applications because of their excellent optical and electrical attributes with minimal toxicity. We synthesized composite films of lead-free Cs₃Bi₂Br₉ perovskite embedded in the polyvinylidene fluoride (PVDF) matrix and have investigated their piezoelectric energy harvesting. Five PVDF@Cs₃Bi₂Br₉ composite films were fabricated with varying wt% of the perovskite in the PVDF. The composite with a 4 wt% of the perovskite shows 85% activation of the electroactive β-phase of PVDF. Additionally, this composite exhibits a maximum polarisation of ∼0.1 μC cm^-2 and the best energy storage density of ∼0.8 mJ cm^-3 at an applied field of ∼16 kV cm^-1 among all the synthesized composites. A nanogenerator fabricated using 4 wt% loading in the composite film produced an instantaneous output voltage of ∼40 V, an instantaneous current of ∼4.1 μA, and a power density of ∼17.8 μW cm^-2 across 10 MΩ resistance when repeatedly hammered by the human hand. The nanogenerator is further employed to light up several LEDs and to charge capacitors with a small active area demonstrating significant promise for prospective wearables and portable devices and paving the way for high-performance nanogenerators using lead-free halide perovskites. Density functional theory calculations were performed to understand the interaction of the electroactive phase of the PVDF with different perovskite surface terminations to unravel the various interaction mechanisms and their ensuing charge transfer properties.

Crystal structure and optical characterization of a new hybrid compound, C6H9N2FeCl4, with large dielectric constants for field-effect transistors

Due to remarkable dielectric features, such as a large dielectric constant, strong electrical conductivity, high capacitance, and low dielectric loss, hybrid materials have lately seen a huge number of applications in the field of optoelectronics. These are critical characteristics that qualify the performance of optoelectronic devices, particularly field-effect transistor components (FETs). Here, the hybrid compound 2-amino-5-picoline tetrachloroferrate(iii) (2A5PFeCl₄) was synthesised by using the slow evaporation solution growth method at room temperature. Structural, optical, and dielectric properties have been investigated. The 2A5PFeCl₄ compound crystallises in the monoclinic system (P2₁/c space group). Its structure can be described as a successive layering of inorganic and organic parts. [FeCl₄]^- tetrahedral anions and 2-amino-5-picolinium cations are connected by N-H⋯Cl and C-H⋯Cl hydrogen bonds. The optical absorption measurement confirms the semiconductor nature with a band gap of around 2.47 eV. Additionally, the structural and electronic properties of the title compound have been investigated theoretically through DFT calculations. At low frequencies, this material has significant dielectric constants (ε ∼10⁶). Furthermore, the high electrical conductivity, low dielectric loss at high frequencies, and high capacitance show that this new material has great dielectric potential in FET technologies. Due to their high permittivity, these compounds can be employed as gate dielectrics.

A computational study of electrical contacts to all-inorganic perovskite CsPbBr3

All-inorganic halide perovskites are promising candidates for optoelectronic devices due to their excellent physicochemical properties and better thermal stability than their hybrid counterparts. The electrical contact to perovskite plays a crucial role in determining the device's performance. This paper investigated the contacts of two types of CsPbBr₃surface to a series of metals (Pd, In, Pb, Zr, Ti, Zn, graphene, and Ti₃C₂) through first-principles calculations. On the PbBr₂-terminated surface, all the studied metals form Schottky contacts with minimum barriers ranging from 0.63 to 0.97 eV. On the CsBr-terminated surface, Ti and Ti₃C₂forms n-type Ohmic contacts while others form Schottky contacts with minimum barriers ranging from 0.25 to 0.97 eV. Ti₃C₂, considering the small Schottky barrier, large tunneling barrier, and high electronic localization function, is found to be proper ohmic metal contacts with the CsBr-terminated surface. In addition, a -16.4% to 15.1% change in the size of the CsPbBr₃band gap is found because of the interfacial interaction. The Fermi pinning factor of the CsPbBr₃-metal contact is estimated via a modified method considering the gap change, and that of the PbBr₂-terminated one is slightly larger than that of the CsBr-terminated one, indicating a more flexible Schottky barrier in the former through changing the metal work function. This work presents a comprehensive understanding of metal contacts to all-inorganic perovskite CsPbBr₃and offers theoretical guidance for preparing high-performance inorganic perovskite photoelectric devices.