Phase Transition Properties Research Articles

Thermodynamics, phase transition and Joule–Thomson expansion of 4-D Gauss–Bonnet AdS black hole

In this paper, we explore the thermodynamic and phase transition properties of asymptotically AdS black holes within Einstein–Gauss–Bonnet gravity, focusing on Joule–Thomson expansion. Thermodynamics is studied in the extended phase space, where the cosmological constant serves as thermodynamic pressure. We observe that the black hole undergoes a phase transition similar to that of a van der Waals system. We analyze charged and neutral cases separately to distinguish the effect of charge and Gauss–Bonnet parameter on critical behavior and examine the phase structure. We find that the Gauss–Bonnet coupling parameter behaves similarly to black hole charge or spin, guiding the phase structure. To understand the underlying phase structure determined by the Gauss–Bonnet coefficient [Formula: see text], we introduce a new order parameter. We discover that the change in the conjugate variable to the Gauss–Bonnet parameter acts as an order parameter, demonstrating a critical exponent of [Formula: see text] in the vicinity of the critical point. Since the phase structure is analogous to that of a van der Waals fluid, we investigate the Joule–Thomson expansion of the black hole. We analytically study the Joule–Thomson expansion, focusing on three key characteristics: the Joule–Thomson coefficient, inversion curves and isenthalpic curves. We obtain isenthalpic curves in the T–P plane and illustrate the cooling–heating regions.

Structural phase transition, relaxor behavior, and ultra-low strain hysteresis in BaTiO3 ceramics modified by BiYO3

In this study, the structural properties, phase transition, relaxor behavior, and strain properties of (1−x)BaTiO3‒xBiYO3 (x= 0.02‒0.15 mol) ceramics were investigated. The room temperature x-ray diffraction and Raman spectroscopy results reveal that (1−x)BaTiO3‒xBiYO3 ceramics undergo phase transition from tetragonal to pseudo-cubic structure with x increasing. The curves of dielectric constant and loss tangent as a function of temperature and frequency show that the dielectric constant was changing from being dependent on temperature to being independent of it upon increasing BiYO3 amount, which is induced obvious dielectric relaxation behavior. Slimmer polarization–electric field (P–E) loops and lower remnant polarization (Pr ) were observed for samples with x ⩾ 0.08. The transition between the ferroelectric and relaxor states leads to the narrow strain–electric field (S–E) loops, which exhibit a high electric field-induced strain of 0.192% and an ultra-low strain hysteresis of 10.4% at an electric field of 70 kV cm−1 for x= 0.04. This excellent performance indicates that 0.96BaTiO3‒0.04BiYO3 ceramic may be promising lead-free materials for high-precision displacement actuators applications.

Phase transition and gel properties of chemically modified cassava starch in choline acetate and water mixtures

This work studied the phase transition and gel properties of cassava starch in aqueous choline acetate ([Ch][OAc]) solution at different [Ch][OAc]:water weight ratios. The paste viscosity and gel strength followed a similar pattern to the starch phase transition temperature, increasing at a 2:3 [Ch][OAc]:water ratio and then decreasing at 3:2 and 4:1 ratios. However, the mobility of free water in the starch gel decreased as the [Ch][OAc]:water ratio increased. At the same [Ch][OAc]:water ratios, acetylated cassava starch (ACS) underwent phase transition more easily than native cassava starch (NCS), leading to greater granule destruction. Nevertheless, ACS gels displayed more viscous-dominated rheological behavior, lower paste viscosity, viscoelasticity, and weaker water-holding capacity (WHC) than NCS gels. In contrast, cross-linked cassava starch (CCS) gels had higher paste viscosity, gel viscoelasticity, and WHC. However, at a 4:1 [Ch][OAc]:water ratio, the viscoelasticity of CCS gel was lower than NCS gel, and the differences in WHC were minimal, likely due to the incomplete phase transition of especially CCS under this condition. Our findings show that starch chemical modification significantly affects phase transition behavior and gel properties in [Ch][OAc]:water mixtures, with outcomes influenced by the viscosity of the aqueous [Ch][OAc] solution and the interaction between [Ch][OAc] and water.

Switchable Vanadium Dioxide Metasurface for Terahertz Ultra-Broadband Absorption and Reflective Polarization Conversion.

Based on the unique insulator-metal phase transition property of vanadium dioxide (VO2), we propose an integrated metasurface with a switchable mechanism between ultra-broadband absorption and polarization conversion, operating in the terahertz (THz) frequency range. The designed metasurface device is constructed using a stacked structure composed of VO2 quadruple rings, a dielectric layer, copper stripes, VO2 film, a dielectric layer, and a copper reflection layer. Our numerical simulations demonstrate that our proposed design, at high temperatures (above 358 K), exhibits an ultra-broadband absorption ranging from 4.95 to 18.39 THz, maintaining an absorptivity greater than 90%, and achieves a relative absorption bandwidth of up to 115%, significantly exceeding previous research records. At room temperature (298 K), leveraging VO2's insulating state, our proposed structure transitions into an effective polarization converter, without any alteration to its geometry. It enables efficient conversion between orthogonal linear polarizations across 3.51 to 10.26 THz, with cross-polarized reflection exceeding 90% and a polarization conversion ratio over 97%. More importantly, its relative bandwidth reaches up to 98%. These features highlight its wide-angle, extensive bandwidth, and high-efficiency advantages for both switching functionalities. Such an ultra-broadband convertible design offers potential applications in optical switching, temperature dependent optical sensors, and other tunable THz devices in various fields.

Structural phase transition and optical properties of zero-dimensional cobalt bromide hybrid material

Zero-Dimensional (0D) metal halide materials have recently emerged as a class of potential optoelectronic materials because of the structural diversity and superior photophysical properties. Here we report a 0D cobalt bromide hybrid material, [Br(CH2)3NH3]2CoBr4 (BPA-CoBr4, BPA=Br(CH2)3NH3, 3-Bromopropylamine), in which the isolated metal halide tetrahedron (CoBr42-) is completely separated each other and surrounded by the organic ligand Br(CH2)3NH3+. Differential scanning calorimetry (DSC) measurements exhibit BPA-CoBr4 undergoes a first-order structural phase transition, as clearly visible to a pair of weak peaks at 340 K (heating) and 317 K (cooling). Single crystal X-ray diffractions were carried out at 293 K and 360 K to explain the phase transformation mechanism, indicating it is an isostructural order–disorder type. The crystal structures which both crystalize in a monoclinic P21/c crystal symmetry and the most distinct difference between room-temperature and high-temperature structures is the order–disorder transition of the 3-Bromopropylamine, which is the driving force of the phase transition. The UV–vis absorption spectra reveal that BPA-CoBr4 has a steep absorption edge at 280 nm corresponding to photo energy of 4.4 eV. The density functional theory (DFT) calculations were performed to study the electronic structure with narrower indirect bandgap 3.9 eV which is lower than the experimental values. PDOS plots show that the electronic states of Co-d and Br-p orbitals are mainly contributed for the VBM and CBM of BPA-CoBr4.

Dimension-Controlled VO2 Film for Optoelectronic Logic Gates and Information Encryption.

As the fields of photonics and information technology develop, a lot of novel applications based on VO2 material, such as optoelectronic computing and information encryption, have been developed. While the performance of these devices was not only closely associated with the VO2 phase transition properties but also depended on their dimensional characteristics. In the current study, we conducted the dimension-controlled vanadium dioxide (VO2) film growth, resulting in the epitaxial 2-dimensional (2D) VO2 film and well-distributed 3-dimensional (3D) VO2 crystal film deposition, respectively. It was revealed that, unlike the 2D film, the pronounced localized surface plasmon resonance dominated the near-infrared spectrum across the phase transition for the 3D VO2 film due to the naturally formed meta-surface structure, which showed a transmittance valley in the infrared spectrum after metallization. Based on this distinct infrared spectrum feature in the 3D VO2 film, we proposed an optoelectronic logic gate controlled by the input voltage and the probing Vis/IR light. By detecting the transmittance states of the probing light with different wavelengths, we achieved multistate encoding functions and demonstrated the information encryption application. This new conception device also showed great potential for some other applications such as optoelectronic coupled computing, information encryption, and optical near-field sensing computing.

Enhanced mechanical and thermophysical properties of Mg2Ca, Al2Ca, and Al4Ca bulk metallic glasses in comparison to crystalline alloys for bone grafting applications: A molecular dynamics investigation

We investigate the glassy-state properties of Mg2Ca, Al2Ca, and Al4Ca from the grafting application viewpoint. We employed classical molecular dynamics to examine the phase transition, structural, thermodynamic, transport, and mechanical properties in the amorphous state. All properties suggest successful simulations of the glass phase at and below the glass transition temperature, ranging between 550 and 689 K for Mg2Ca, Al2Ca, and Al4Ca. Computed results are compared and discussed with the reported findings and known mechanical and thermal properties of the various parts of the human bones and biocomposites. The comparison establishes that the mechanical, thermal, and transport properties significantly improve in the glass phase compared to its crystalline alloy form. At 300 K, studied glasses have densities in close agreement with human bone density. Structural analysis and heat capacity show the second-order phase transition, verifying the formation of the glass structure. The targeted glasses exhibit excellent thermal conductivity and thermal diffusivity compared to other commonly used biocomposites for bone grafting. Furthermore, the simulated elastic properties, viz., the Poisson ratio, G/B ratio, Cauchy's pressure, and yield strength, are in close agreement with the mechanical properties of various parts of human bone. The predicted ductility nature, contrary to the brittle character of Mg2Ca, Al2Ca, and Al4Ca crystalline alloys, proves the superiority of the glassy form for the implant's functioning. The minimum enthalpy of formation and thermodynamic stability of studied compounds benefit the synthesis process; hence, we propose that the studied glasses are persuasive materials for experimental synthesis aimed at bone grating applications.

Multicaloric Cryocooling Using Heavy Rare-Earth Free La(Fe,Si)13-Based Compounds.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable. Here, we aim to mitigate this limitation through the utilization of a multicaloric cooling concept, which uses the external stimuli of isotropic pressure and magnetic field to tailor and induce magnetostructural phase transitions associated with large caloric effects. In this study, La0.7Ce0.3Fe11.6Si1.4 is used as a nontoxic, low-cost, low-criticality multiferroic material to explore the potential, challenges, and peculiarities of multicaloric cryocooling, achieving maximum isothermal entropy changes up to -28 J (kg K)-1 in the temperature range from 190 K down to 30 K. Thus, the multicaloric cooling approach offers an additional degree of freedom to tailor the phase transition properties and may lead to energy-efficient and environmentally friendly gas liquefaction based on designed-for-purpose, noncritical multiferroic materials.

The electrical properties of nitrogen-doped vanadium dioxide thin films grown by magnetron sputtering

Abstract Vanadium dioxide (VO2) undergoes a reversible semiconductor-metal phase transition near 68°C, and the optical and electrical properties could be changed in femtoseconds. These unique characteristics meet the electro-optic switch applications. In this work, to improve the intrinsic characteristics of VO2, a series of nitrogen-doped vanadium dioxide thin films were prepared by reactive magnetron sputtering. Moreover, the effects of different nitrogen flow rates on the microstructure, surface morphology, electrical properties and phase transition properties of the samples were investigated. The samples are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), four-point probe system, and Hall effect et al. Sheet resistance variation at room temperature and high temperatures indicates remarkable semiconductor-metal transition characteristics. According to results of Hall effect measurement, when nitrogen flow rate is less than 1 sccm, the samples exhibits p-type semiconductor characteristics. However, while nitrogen flow rate reaches 1 sccm, n-type semiconductor characteristics appear. What’s more, Carrier mobility reaches a maximum at a nitrogen to oxygen flow ratio of 0.3. The results reveal that the samples have a great potential on electro-optic switching applications.

Active tunable terahertz multifunctional device switching from multiple narrowband perfect absorption to plasma-induced transparency

This paper puts forward a terahertz multifunctional device based on reversible phase transition property of VO2, which can realize active switching from multiple narrowband perfect absorption to plasma-induced transparency (PIT). By means of impedance matching theory and electric field distributions, we analyze the mechanism behind three absorption formants, and the absorption spectrum is consistent with data obtained from coupled mode theory. Three perfect absorption formants at the frequencies of 4.37 THz, 5.27 THz and 6.1 THz are extremely sensitive to the changes in external environment, which possesses a higher sensitivity up to 1.29 THz/RIU and FOM up to 9.45, indicating prominent sensing performance. By regulating the Fermi energy in a unified manner, three absorption formants can be observed within a specific frequency range. When the Fermi energy of three graphene patterns is individually manipulated, trimodal narrowband perfect absorption will transform into one bimodal and two unimodal ones. While the device is under PIT operation mode, two transmission windows are formed at 5.1 THz and 5.92 THz. It can be concluded that dual PIT arises from the mutual coupling between two bright modes and a dark mode formed by patterned graphene, when combined with the transmission spectra and the corresponding electric field distributions. Similarly, the modulation of graphene Fermi energy can realize dynamic tuning of the transmission performance, and single PIT can be achieved when graphene patterns are regulated separately. In summary, the proposed device can meet various functional requirements for multiple perfect absorption and PIT under different conditions and promote developments of terahertz technology in fields of environmental detection, electromagnetic modulation, multi-function devices and other application.

CFD simulation of novel adaptive pin-fins microchannel heat sink to improve thermal management of electronic chips

Frequent hotspots pose a significant challenge for chip thermal management. Conventional microchannel with fixed structure cannot deal with random hotspots, which appear in irregular time and space. To address random hotspots and reduce microchannel energy consumption, a novel adaptive pin-fins microchannel (A-MCHS) is proposed in this paper to intelligently tackle with the hotspot region, which consists of a number of pin-fins with property of phase transition and volume shrinkage when the temperature is raised to 313.15 K. A CFD method is applied to study its thermal performance and user defined function (UDF) is used to realize the adaptive thermal response of pin-fins. It’s found that the adaptive pin-fins of the hotspot undergo volume reduction and enlarged local coolant flow under higher hotspot heat flux, illustrating the automatic and adaptive flow regulation effect. Compared with the fixed pin–fin microchannel, the local heat transfer performance of A-MCHS in the hotspot region is enhanced by 37.9 %, average Nu of the microchannel is advanced by 7.4 %, and the maximum chip surface temperature is reduced by up to 3.12 K. Moreover, it also shows a significant reduction of 10.7 % in pressure drop, suggesting a great energy saving in pumping cooling fluid. It’s indicated that the adaptive pin-fins microchannel provides efficient cooling and intelligently enhanced thermal management and energy saving for high heat flux electronic chips.

Exploring structural phase transition, electronic and optical characteristics of optoelectronic phosphides XSiP2 (X = Mg, Cd, and Zn) through First principle computation.

The present study reports the properties of pressure-induced phase transition, electronic and optical of phosphides XSiP2 under pressure in chalcopyrite, sodium chloride (rock salt), and Wurtzite phases. The study shows the chalcopyrite phase as the most stable phase among the other studied phases. The obtained structural parameters in the chalcopyrite and rock-salt phases reasonably agree with the literature. The computed band structures revealed a semiconductor behavior in chalcopyrite structure and metallic behavior for rock- salt and wurtzite structures. In the energy range of 0 to 30eV, optical parameters such as the real and imaginary parts of the dielectric constant, refractive index, and reflectivity are calculated and compared with existing data. Our optical properties findings are predictive for the rock-salt and wurtzite phases. Since no results are available in the literature, these results may serve as references for other theoretical and experimental studies. The calculations are performed by employing the "full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT)."

A Coordinating Small Organic Molecule with Tunable Lower Critical Solution Temperature for Efficient Management of Solar Radiation.

Structurally well-defined small molecules with lower critical solution temperature (LCST) behavior offer enormous prospects for fine-tuning their phase transition properties to be "on-demand" applied in the specific scene but are still underexplored. Herein, a novel amphiphilic small LCST molecule is rationally designed and synthesized. The molecule, namely TG, features a conjugation of multiple short ethylene glycol (EG) chains with the functional coordinating terpyridine (Tpy) moiety. The molecule TG demonstrates excellent LCST behavior down to 0.05× 10-3 m in a water solution. And a cloud point Tcp = 30.9°C with a very short thermal hysteresis ΔT = 0.2°C and good reversibility can be achieved when c = 0.1× 10-3 m. The excellent LCST properties of TG have enabled its successful performance as the smart window for solar radiation management with the ∆Tlum, ∆TIR, and ∆Tsol being 83.6%, 49.1%, and 67.2%, respectively. Moreover, the presence of Tpy moiety in TG enables its coordination with Ru3+ and the resulting complex also exhibits modulated LCST behavior with different concentration-dependent Tcp. These studies would provide novel small-molecule-based scaffolds for constructing better solar radiation management systems as well as other thermal-responsive smart materials.

Effect of methylene lengths of 4-(ω-(methylimidazole)-alkyloxy)-4’-(cyano)-biphenyl on cellulose liquid crystal solution and its phase transition properties

Effect of methylene lengths of 4-(ω-(methylimidazole)-alkyloxy)-4’-(cyano)-biphenyl on cellulose liquid crystal solution and its phase transition properties

Uniaxial Symmetry Breaking in Bacteriorhodopsin at the Thermal Phase Transition of Lipids of Purple Membranes.

The article correlates between symmetry breaking and phase transition. An analogy, extending from physics to biology, is known to exist between these two topics. Bacteriorhodopsin (bR) as a paradigm of membrane proteins has been used as a case study in the present work. The bR, as the sole protein embedded in what is called a purple membrane (PM), has attracted widespread interest in bionanotechnological applications. The lipids of PM have a crucial role in maintaining the crystal lattice of bR inside PM. For this reason, the present work has been concerned with elucidating the thermal phase transition properties of the PM lipids in orthogonal directions. The results indicated that the axial symmetry of bR exhibits considerable changes occurring at the thermal phase transition of lipids. These changes are brought by an anomaly observed in the time course of orthogonal electric responses during the application of thermal fields on PM. The observed anomaly may bear on symmetry breaking in bR occurring at the phase transition of lipids based on such analogy found between symmetry breaking and phase transition. Lipid-protein interactions may underlie the broken axial symmetry of bR at such lipid thermal transition of PM. Accordingly, thermally perturbed axial symmetry of bR may be of biological relevance relying on the essence of the crystal lattice of bR. Most importantly, a question has to be raised in the present study: Can bR, as a helical protein with broken axial symmetry, affect the symmetry breaking of helical light? This may be of potential technical applications based on a recent discovery that bR breaks the symmetry of helical light.

Switchable dual ultra-broadband perfect absorber based on graphene and vanadium dioxide hybrid metamaterials

The phase transition property of vanadium dioxide (VO2) makes it an attractive field in temperature-controlled chips. In this paper, a microstructure based on a graphene disk and a ring-shaped VO2 hybrid metamaterial is proposed to achieve switchable dual ultra-broadband perfect absorption in the terahertz region, which is analyzed by the phase transition property of VO2 and the dynamic electrical regulation of graphene. When the graphene disk is not present, the absorption intensity can reach up to 97.07%. When the graphene disk is present and respectively interacts with the VO2 metallic and insulated phases, the results exhibit an ultra-broadband perfect absorption (>90%) from 1.620 THz to 4.533 THz and from 1.506 THz to 3.576 THz, respectively, where the bandwidths are as high as 2.913 THz and 2.070 THz, respectively. Adjusting the Fermi level of graphene and the VO2 conductivity allows the absorption intensity and bandwidth to be effectively controlled, where the fractional bandwidth from 81.46% to 94.69% and a high modulation depth of 95.09% can be achieved. These results suggest that dual ultra-broad perfect absorption can be dynamically switched within a single absorber and has various modulation means, which are expected to be developed in applying multifunctional modulators.

Correlation between the structural phase transition and magnetic properties of sol-gel synthesized nanoparticles

The La2CoFeO6 (LCFO) nanoparticles were synthesized using the sol-gel method and calcined at 600 , 800 , and 1000 . The X-ray diffraction data confirm the successful formation of LCFO nanoparticles. The crystallite size was observed to increase from ∼13 nm to ∼26 nm as the calcination temperature rose. Detailed Rietveld analysis revealed the coexistence of both orthorhombic (Pnma: S.G. 62) and rhombohedral ( : S.G. 167) phases in the LCFO samples. A two-phase Rietveld refinement demonstrated a structural phase transition (from Pnma to ) as the calcination temperature increased. FESEM micrographs exhibited a granular morphology for the LCFO nanoparticles, and the grain size was observed to increase with the elevated calcination temperature. Magnetization curves illustrated an increase in magnetization with a decrease in crystallite size or a reduction in calcination temperature for LCFO nanoparticles. At higher calcination temperatures, the rhombohedral phase displayed significant antisite disorder, resulting in the disruption of long-range ferromagnetic ordering in the material and a subsequent decrease in maximum magnetization.

Tunable mid-infrared broadband absorption in the atmospheric window of wavelength in 3–5 μm using VO2 phase transition in a three-layer metamaterial

Tunable metasurfaces have garnered considerable attention for their remarkable ability to manipulate electromagnetic waves within carefully designed nanostructures. Achieving resonant absorption requires precise control over the geometry and size of micro-nano structures. This study introduces a highly versatile metasurface platform that leverages the unique phase transition properties of vanadium dioxide (VO2) for controlled absorption. Our design features a planar layered structure with a 0.1 μm thick VO2 top layer, enabling tunability in both thermal and intensity aspects. We demonstrate significant tuning of broadband light absorption across the mid-infrared spectrum, with absorption rates ranging from approximately 30 %–98 % in the critical atmospheric infrared window of 3–5 μm. This range is crucial for infrared sensing, imaging, and communication applications. Notably, the absorption rate increases as the temperature decreases, indicating a positive shift in dynamics, for which we provide a physical explanation. Numerical simulations highlight the ability to control absorption bandwidth by adjusting the thickness and temperature of VO2 layer. These adaptable broadband absorbers hold significant promise for a diverse range of applications, including absorption filters, thermal emitters, thermos photovoltaics, and thermal imaging. Furthermore, the introduced thermally switchable, spectrally selective metamaterials can find applications in dynamic infrared camouflage and active radiative thermal management, opening new horizons in the realm of metamaterial-based technologies.

Multi-functional and actively tunable terahertz metamaterial absorber based on graphene and vanadium dioxide composite structure

In this paper, a fabrication friendly terahertz (THz) metamaterial hybrid absorber comprised of square-shaped graphene and U-shaped vanadium dioxide is proposed and numerically analyzed. This device can be tuned dynamically to function as a wide-broadband, reduced-broadband, multi-band, or perfect single-band absorber. Switchable qualities are achieved through simultaneous tuning of the electrical properties of graphene and the phase transition properties of vanadium dioxide. The theory behind the absorption is explored using the distribution of the electric field and the theory of impedance matching. It is clear from the simulation results that the suggested structure can perform as a wide-broadband absorber for the transverse electric (TE) wave during the insulating phase of vanadium dioxide. In this case, graphene’s Fermi energy is configured to 0.7 eV, and it has a 0.1 ps relaxation time. Moreover, only changing the relaxation time to 0.5 ps enables the identical structure to perform as a multi-band absorber. On the contrary, the designed structure exhibits a reduced broadband absorption for the TE wave when the vanadium dioxide is thermally tuned to a metallic state and graphene’s Fermi energy is configured to 0 eV with a 0.1 ps relaxation time. Moreover, by inducing the metallic state in vanadium dioxide and adjusting the Fermi energy of graphene to 0.3 eV with a 0.1 ps relaxation time, the structure performs as a single-band perfect absorber. The main advantage of this work is that the proposed absorber device can be operated as a single-band, multi-band, or broadband absorber with two different bandwidths by applying external voltage and changing temperature. Additionally, for both the TE and transverse magnetic (TM) waves, the structure retains a high level of absorption until 40° of incident angle. Finally, due to its multi-functional property, simple geometric structure, and actively adjustable function, the presented structure has possible real-life applications in the terahertz frequency range.

Three-Dimensional Bimetallic Ammonium K-Eu Nitrate with a Rare (6,6)-Connected Ion Topology Exhibiting Structural Phase Transition and Photoluminescence Properties.

A K-Eu bimetallic ammonium metal-nitrate three-dimensional (3D) framework incorporating R-N-methyl-3-hydroxyquinuclidine, (RM3HQ)2KEu(NO3)6 (RM3HQ = R-N-methyl-3-hydroxyquinuclidine, 1), was characterized and reported. Distinguishing from the former hybrid rare-earth double perovskites, 1 adopts a mixed corner- and face-sharing K+/Eu3+-centered polyhedral connectivity to form a 3D inorganic framework, showing a rare (6, 6)-connected ion topology with a 66 framework. Notably, 1 exhibits clear phase transition, and the switchable thermodynamic behavior is confirmed by variable-temperature dielectric measurements and second-harmonic generation response. Moreover, 1 also shows photoluminescence properties. The activator Eu3+ plays a crucial role in this process, leading to a significant narrow emission at 592 nm with a photoluminescence quantum yield (PLQY) of 20.76%. The fluorescence lifetime (FLT) of 1 is 4.32 ms. This finding enriches the bimetallic hybrid system for potential electronic and/or luminescence applications.