Metal-halide perovskites (MHPs) exhibit excellent properties for application in optoelectronic devices. The bottleneck for their incorporation is the lack of long-term stability such as degradation due to external conditions (heat, light, oxygen, moisture, and mechanical stress), but the occurrence of phase transitions also affects their performance. Structural phase transitions are often influenced by phonon modes. Hence, an insight into both the structure and lattice dynamics is vital to assess the potential of MHPs. In this study, GIWAXS and Raman spectroscopy are applied, supported by density functional theory calculations, to investigate the apparent manifestation of structural phase transitions in the MHP CsPbBr3. Macroscopically, CsPbBr3 undergoes phase transitions between a cubic (α), tetragonal (β), and orthorhombic (γ) phase with decreasing temperature. However, microscopically, it has been argued that only the γ phase exists, while the other phases exist as averages over length and time scales within distinct temperature ranges. Here, direct proof is provided for this conjecture by analyzing both theoretical diffraction patterns and the evolution of the tilting angle of the PbBr6 octahedra from molecular dynamics simulations. Moreover, sound agreement between experimental and theoretical Raman spectra allowed to identify the Raman active phonon modes and to investigate their frequency as a function of temperature. As such, this work increases the understanding of the structure and lattice dynamics of CsPbBr3 and similar MHPs.

Metal halide perovskite (MHP) quantum dots (QDs) offer immense potential for several areas of photonics research due to their easy and low‐cost fabrication and excellent optoelectronic properties. However, practical applications of MHP QDs are limited by their poor stability and, in particular, their tendency to aggregate. Here, we develop a two‐step double‐solvent strategy to grow and confine CsPbBr₃ QDs within the three‐dimensional (3D) cavities of a mesoporous SBA‐16 silica scaffold (CsPbBr₃@SBA‐16). Strong confinement and separation of the MHP QDs lead to a relatively uniform size distribution, narrow luminescence, and good ambient stability over 2 months. In addition, the CsPbBr₃@SBA‐16 presents a high activity and stability for visible‐light‐driven photocatalytic toluene C(sp³)–H bond activation to produce benzaldehyde with ∼730 µmol g⁻¹ h⁻¹ yield rate and near‐unity selectivity. Similarly, the structural stability of CsPbBr₃@SBA‐16 QDs is superior to that of both pure CsPbBr₃ QDs and those confined in MCM‐41 with 1D channels.

In this paper, a comparative structural, dielectric, and magnetic study of two langasite compounds Ba₃TeCo₃P₂O₁₄ (absence of lone pair) and Pb₃TeCo₃P₂O₁₄ (Pb²⁺ 6s² lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in the presence of a stereochemically active lone pair. In the case of Pb₃TeCo₃P₂O₁₄, mixing of both Pb 6s with Pb 6p and O 2p helps the lone pair to be stereochemically active. This stereochemically active lone pair brings a large structural distortion within the unit cell and creates a polar geometry, while the Ba₃TeCo₃P₂O₁₄ compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric fields confirms room temperature ferroelectricity for Pb₃TeCo₃P₂O₁₄, which was not the case for Ba₃TeCo₃P₂O₁₄. A detailed study was carried out to understand the microscopic mechanism of ferroelectricity, which revealed the exciting underlying activity of a polar TeO₆ octahedral unit as well as Pb-hexagon.

Frustrated magnets offer a plethora of exotic magnetic ground states, including quantum spin liquids (QSLs), in which enhanced quantum fluctuations prevent a long-range magnetic ordering of the strongly correlated spins down to lowest temperature. Here we have investigated the trimer based mixed valence hexagonal rhodate ${\mathrm{Ba}}_4{\mathrm{NbRh}}_3{\mathrm{O}}_{12}$ using a combination of dc and ac magnetization, electrical resistivity, specific heat, and muon spin rotation/relaxation ($\mu \mathrm{SR}$) measurements. Despite the substantial antiferromagnetic exchange interactions, as evident from the Weiss temperature (${\theta }_{\mathrm{W}}\sim -35$ to $-45\mathrm{K}$), among the Rh-local moments, neither long-range magnetic ordering nor spin freezing is observed down to at least 50 mK, in ac-susceptibility, specific heat, and zero-field $\mu \mathrm{SR}$ measurements (down to 0.26 K). We ascribe the absence of any magnetic transition to enhanced quantum fluctuations as a result of geometrical frustration arising out of the edge-sharing equilateral Rh-triangular network in the structure. Our longitudinal-field $\mu \mathrm{SR}$ result evidences persistent spin fluctuations down to 0.26 K, thus stabilizing a dynamic QSL ground state in ${\mathrm{Ba}}_4{\mathrm{NbRh}}_3{\mathrm{O}}_{12}$. Furthermore, the magnetic specific heat data at low $T$ reveal a significant $T$-linear contribution plus a quadratic $T$ dependence, which may indicate the gapless Dirac QSL phenomenology of the spinon excitations with a linear dispersion.