Large size and high quality single crystals are the prerequisite to fully evaluate their physical properties and potential technical applications. Herein, centimeter-sized KCsMoP₂O₉ (KCMP) crystals were successfully grown using the Kyropoulos method. The value of the full width at half maximum (36′′) indicated that the grown KCMP crystals were of high quality. The type of phase transition for KCMP crystals was found to be incommensurate to prototypic transition by in situ X-ray diffraction, and the phase transition mechanism was studied using a rigid unit mode approach. In addition, the linear and nonlinear optical properties of KCMP crystals were studied, and an efficient 515 nm second harmonic laser was successfully achieved in nonbirefringent-matched KCMP crystals using the emerging additional periodic phase technology.

Effective doping plays an important part in the marketization of gallium nitride (GaN) devices.

The dimensionless figure of merit ZT is the key metric for quantifying thermoelectric performance; however, its optimization is inherently limited by the intrinsic coupling between electrical and thermal transport properties. Herein, we perform first-principles calculations using the temperature-dependent effective potential method to investigate cation alloying in SnSe, where Sn2+ ions were randomly substituted by aliovalent cations - specifically Na+ and Sb3+ - a strategy that induces chemical bond synergy in NaSn2SbSe4, effectively decoupling electronic and phonon transport behaviors. Random cation occupation induces a mixed covalent-ionic bonding character, generating local bond-strength fluctuations that act as phonon-scattering centers. Furthermore, localized Sb-Se and Sn-Se antibonding states below the Fermi level correlate with the softening of low-frequency optical phonon branches. Combined with pronounced lattice anharmonicity, this phonon softening significantly enhances four-phonon scattering rates and suppresses the lattice thermal conductivity. Concurrently, aliovalent cation incorporation promotes electron delocalization between Sn-5p and Se-4p orbitals and strengthens covalent bonding character. This modified orbital hybridization alters band dispersion, reducing the hole effective mass while preserving high electrical conductivity in NaSn2SbSe4. The optimal balance between low lattice thermal conductivity and high power factor yields superior thermoelectric performance for NaSn2SbSe4 relative to SnSe across the entire temperature range, with a peak ZT of 0.88 at 800 K. This study establishes chemical bonding engineering as a promising strategy for enhancing thermoelectric performance and provides guidance for exploring high-performance high-entropy thermoelectric materials.