Reversible Phase Transition Research Articles

Being Smarter, Azobenzene-Containing Biomaterial Showing Triple Stimuli-Responsive Phase Change Property to Light, Humidity and Force at Room Temperature.

Multiple stimuli-responsiveness is an attractive property that is studied in physical chemistry and materials chemistry. While, multiple stimuli-responsive phase change in an isothermal way is rarely addressed for functional materials at room temperature. In this study, one azobenzene-containing surfactant AZO is designed for the fabrication of triple stimuli-responsive phase change biomaterial (Alg-AZO) through the electrostatic complexation with natural alginate. Thanks to the photoisomerization ability, molecular flexibility and hydrophilicity of AZO, together with the tailoring effect of alginate on AZO, Alg-AZO could perform reversible isothermal phase transition between liquid crystalline and isotropic liquid states under the stimuli of either light or humidity at room temperature. Furthermore, the humidity-induced isotropic state can also fast transit to ordered state under shear force, owing to the π-π interactions between planar trans-AZO in Alg-AZO material. With good biocompatibility, self-healing property and in vivo wound healing promoting capacity that is promoted by light, humidity and force, Alg-AZO would be suitable for working as a new smart biomaterial in biological and biomedical areas. This work provides a designing strategy for gaining multiple stimuli-responsive smart materials based on biomacromolecules, and also opening a new opportunity for gaining self-healing biomaterials capable of working in various conditions.

A new organic–inorganic chloride (H3N–(CH2)6–NH3)[SnCl6]: Crystal structure, thermal analysis, vibrational study, and electrical properties

In this work, a new Organic-Inorganic chloride (H3N–(CH2)6-NH3)[SnCl6] (1) has been synthesized and characterized by single crystal X-ray diffraction (XRD), IR, Raman and impedance spectroscopies. The crystallographic study displays that the title compound crystallizes in the triclinic system with the P−1 space group. The vibrational study (IR, Raman) at room temperature confirmed the existence of the organic and inorganic functional groups. Differential scanning calorimetry (DSC) analysis reveals the existence of three reversible phase transitions at T1 = 345/325 K, T2 = 483/443 K, and T3 = 496/465 K (Heating/Cooling). Furthermore, the conductivity analysis and the dielectric properties confirm the presence of these phase transitions. AC-conductivity measurement of (1) has been investigated using complex impedance spectroscopy in frequency and temperature range 10 Hz–5 MHz and 313–523 K, respectively. The study of Nyquist plots showed the contribution of grains and grain boundaries in the electrical study, confirming the existence of a non-Debye type relaxation. The AC conductivity shows that the material has the potential of impedance sensors.

High-Pressure Behavior of NdF3: Structural and Photoluminescence Properties

Abstract This paper investigates the pressure-induced photoluminescence properties and structural phase transitions of functional material NdF3 at room temperature using diamond anvil cell (DAC), in-situ photoluminescence technology, and simulation calculations. Under hydrostatic experimental pressure and simulated pressure up to 20 GPa, the photoluminescence spectra, lattice parameters, and bond lengths of NdF3 were obtained, showing their variations with pressure. Experimental results show that a new emission line, corresponding to the 4F3/2→4I9/2 transition of Nd3+ ions, appears around 12 GPa and persists up to the highest pressure of the experiment. Upon decompression, the new emission line disappears, indicating a reversible phase transition. Notably, from 0 to 12 GPa, the emission intensity of NdF3 decreases significantly under pressure, which may be attributed to the increased energy of lattice phonons in the compressed crystal (shorter Nd-F bonds), leading to enhanced phonon-assisted non-radiative relaxation.

Three-dimensional perovskite (1,4-3.2.2-H2dabcn)CsBr3·H2O showing reversible phase transition, dielectric anomaly and second harmonic generation effect

Three-dimensional perovskite (1,4-3.2.2-H2dabcn)CsBr3·H2O showing reversible phase transition, dielectric anomaly and second harmonic generation effect

Enhancing the Purification and Stability of Superoxide Dismutase by Fusion with Thermoresponsive Self‐Assembly of Elastin Like Polypeptide

AbstractElastin‐like polypeptide (ELP) is a thermo‐sensitive biosynthetic polymer composed of a Val‐Pro‐Gly‐Xaa‐Gly repeating unit possessing a sharp reversible phase transition property at specific temperatures. Here, ELP was fused to human superoxide dismutase 1 (hSOD1) modified with His tag to produce recombinant hSOD1‐Linker‐ELP‐His (hSODLEH) which was expressed in E. coli and purified via inverse thermal cycling (ITC) and Ni‐NTA resin. The results showed that ELP tag did not affect the soluble expression of SOD1. The purification by ITC was superior to Ni‐NTA resin due to its convenient purification process, improved recovery rate and purification fold, thus indicating industrial suitability for large scale protein purification in a cost‐ and time‐efficient manner. Moreover, one round of ITC was sufficient for the recovery of highly purified recombinant SOD. The results further showed that ELP improved the stability of the SOD, and did not affect its secondary structure nor its ability to bind divalent metal ions. Overall, ELP‐protein fusion system could be a promising tool for large scale enzyme purification.

A dynamically switchable and tunable metamaterial device based on vanadium dioxide and Dirac semimetal

In this paper, a dual-function metamaterial device based on vanadium dioxide (VO2) and Dirac semimetal (DS) operating in terahertz (THz) frequency range is designed. The reversible phase transition properties of VO2 are exploited to achieve the dynamic switch between the function of broadband absorption and broadband polarization conversion. It is demonstrated that when VO2 is in the metallic state and the Fermi energy level () of DS is set to 30 the broadband absorption in the operating frequency range of 1.42-3.40 THz can be achieved, and its absorbance exceeds 90% with a relative bandwidth of 82.16%. When VO2 is in the insulating state and the of DS is set at 180 , the high efficient broadband polarization conversion can be obtained in the operating frequency range of 2.08-4.88 THz and the polarization conversion ratio (PCR) is greater than 90% with a relative bandwidth of up to 80.46%. Therefore, the proposed switchable dual-functional THz device can be extensively utilized in absorption, polarization conversion and other potential fields.

Intelligent hybrid hydrogel with nanoarchitectonics for water harvesting from acidic fog

With the development of society, the demand for water resources has risen has increased sharply, and water shortage is becoming a huge challenge to mankind. Therefore, it is extremely urgent to develop a convenient, low-cost, and environmentally friendly fog harvesting material. In this work, inspired by lotus stem with efficient water transport characteristics, the intelligent hybrid hydrogel (IHH) synergistically combines the characteristics of the pH-sensitive PDMAEMA polymer chain and thermo-switchable PNIPAM polymer chain, which simultaneously realizes superior efficient acidic fog uptake (∼6.5 g/g), high-density acidic fog storage, ultra-fast clean water releasing in the efficiency of ∼90 % for 12 min at 60 °C and high cycling stability (∼25 cycles). It is mainly attributed that the amine groups of the PDMAEMA chains are protonated under acidic state, and further the hydration is enhanced, and thus resulting the hydrogel to absorb the acid fog and swell. The PNIPAM polymer can achieve a rapidly reversible phase transition from a hydrophilic state to a hydrophobic one when the temperature beyond LCST, achieving the water releasing quickly. This IHH achieves preliminary water purification, which converts the harvested acidic fog into clean water as the freshwater generator. The IHH offers an insight into the design of novel materials that serve as the freshwater generator in complex environments of practical applications such as fog harvesting devices or systems.

Vertically stacked heterostructure in MoS2/rGO to accelerate ion diffusion kinetics for aqueous zinc ion batteries

The two-dimensional (2D) layered MoS2 is highly desirable as a host cathode material for aqueous zinc ion batteries (AZIBs) due to the typical lamellar structure bonded with weak van der Waals interlayer forces. Nevertheless, sluggish kinetics of Zn2+ diffusion in MoS2 usually leads to inferior Zn2+ storage capability. Herein, a vertically stacked heterostructure of reduced graphene oxide (rGO) and 1 T-2H phase mixed MoS2 (1 T-2H MoS2/rGO) is successfully realized through a bottom-up assembly method. The presence of graphene in the interlayer of MoS2 not only increases the interlayer spacing but also induces the phase transition of MoS2. The flower-like nanocomposite is featured with expanded interlayer spacing of 9.6 Å, abundant 1 T phase, and good hydrophilicity, which facilitate Zn2+ diffusion, charges transfer and electrolyte infiltration. Consequently, the 1 T-2H MoS2/rGO based AZIB achieves exceptional electrochemical performance: admirable specific capacity of 294.6 mAh g−1 at 0.2 A g−1, good rate capability (130.9 mAh g−1 at 4 A g−1), and excellent long-term stability (96.8 % capacity retention after 1600 cycles at 3 A g−1). Experimental and density functional theory (DFT) calculation results reveal that the vertical-stacked structure of MoS2/rGO accelerates Zn2+ diffusion kinetics and charges transfer by reducing the ions migrate energy barrier and band gap. The multiple ex situ characterizations demonstrate that the Zn2+ insertion/extraction process is accompanied by highly reversible phase transition between 2H and 1 T MoS2. This bottom-up assembly strategy can be extended to design more 2D materials with vertically stacked heterostructure as cathodes for high-performance AZIBs.

A three-in-one strategy of high-entropy, single-crystal, and biphasic approaches to design O3-type layered cathodes for sodium-ion batteries

O3-type layered oxides are promising cathodes for sodium-ion batteries (SIBs). However, severe volume changes, irreversible phase transitions, and sluggish Na+ ion transport kinetics lead to structural collapse and severe capacity loss. Herein, a three-in-one strategy “high entropy, single crystal, and biphase” is proposed to design O3-type layered cathodes for SIBs, which achieves enhanced structural stability and Na+ transport kinetics by the combination effect of multimetal high-entropy, the single crystal, and Li substitution. The as-prepared high-entropy oxide (HEO) cathode, Na(Fe1/6Co1/6Ni1/6Mn1/6Ti1/6)Li1/6O2, exhibits a high reversible capacity of 140.3 mAh g−1, robust cycling stability, exceptional rate capability (86 mAh g−1 at rates of 15C), excellent air-stability, and water-resistance ability. In situ X-ray diffraction reveals that the HEO cathode has highly reversible phase transitions and small volume change (ΔV=3.28 %). Ex situ X-ray absorption spectroscopy reveals that reversible Ni2+/Ni4+, Fe3+/Fe3.6+, and Co3+/Co3.6+ redox couples provide charge compensation for the high-entropy cathode at 2.0∼4.2 V. Notably, the full-cell battery based on the high-entropy cathode and hard carbon anode delivers a specific capacity of 134.3 mAh g−1 and an energy density of 390.8 Wh kg−1. This work provides valuable insights into the design of novel high-performance high-entropy cathodes for SIBs, highlighting a promising avenue for advancing rechargeable battery technology.

Unusual Triple-State Switching of Thermally Induced Birefringence in a Two-Dimensional Perovskite Ferroelectric.

Birefringent crystals hold a significant position in optical and optoelectronic fields due to their capability to control polarized light. Despite various chemical strategies devoted to designing birefringent crystals, it remains a challenge to switch and manipulate birefringence under physical stimuli. Here we present an unusual triple-state switching of birefringence in a 2D perovskite ferroelectric, (N-methylcyclohexylammonium)2PbCl4 (1), which exhibits two reversible phase transitions at 361 and 373 K. The in-plane birefringence of 1 (Δnbc) shows three distinctive states inside the bc plane, namely, the low-, high-, and zero-Δnbc states. Strikingly, a huge augmentation of Δnbc is solidly confirmed up to ∼400% between its low and high states, far beyond other birefringent materials. The origin of this triple-state switching of birefringence involves the variation of the ferroelastic strain and domain in the vicinity of the phase transition. As an entirely new mode of switching birefringence, this work facilitates the further development of new intelligent nonlinear optics.

High-quality VO2 thin films sputter-deposited on borosilicate glass substrates for modulating solar transmission and thermal emission

M1-phase VO2 exhibits a reversible phase transition between the insulating and metallic states at T = ∼341 K, and VO2-based smart windows have been extensively studied. The smart window application requires the growth of high-quality VO2 films with a large resistivity change and small hysteresis width (ΔT) on glass substrates using a scalable deposition method such as sputtering. However, the polymorphic nature of VO2 makes it challenging to obtain high-quality VO2 films on ordinary window glasses (borosilicate and soda-lime glasses). Thus far, VO2 films sputtered on glass substrates have exhibited resistivity changes of 1.5–2 orders of magnitude and ΔT = 3–19 °C. In this study, we show that high-quality VO2 films with a resistivity change of 2.5−3.0 orders of magnitude and ΔT = 2 °C can be grown on borosilicate glass substrates via radio-frequency sputtering followed by thermal annealing. The simultaneous achievement of such a large resistivity change and small hysteresis width is highly encouraging not only for smart windows but also for other applications. With respect to the modulation of solar transmission and thermal emission with temperature, the performance levels of the produced VO2 films were 70−75 % of those expected from pure M1-phase VO2 films.

Programming Hydrogen Bonds for Reversible Elastic-Plastic Phase Transition in a Conductive Stretchable Hydrogel Actuator with Rapid Ultra-High-Density Energy Conversion and Multiple Sensory Properties.

Smart hydrogels have recently garnered significant attention in the fields of actuators, human-machine interaction, and soft robotics. However, when constructing large-scale actuated systems, they usually exhibit limited actuation forces (≈2kPa) and actuation speeds. Drawing inspiration from hairspring energy conversion mechanism, an elasticity-plasticity-controllable composite hydrogel (PCTA) with robust contraction capabilities is developed. By precisely manipulating intermolecular and intramolecular hydrogen-bonding interactions, the material's elasticity and plasticity can be programmed to facilitate efficient energy storage and release. The proposed mechanism enables rapid generation of high contraction forces (900kPa) at ultra-high working densities (0.96MJm-3). Molecular dynamics simulations reveal that modifications in the number and nature of hydrogen bonds lead to a distinct elastic-plastic transition in hydrogels. Furthermore, the conductive PCTA hydrogel exhibits multimodal sensing capabilities including stretchable strain sensing with a wide sensing range (1-200%), fast response time (180ms), and excellent linearity of the output signal. Moreover, it demonstrates exceptional temperature and humidity sensing capabilities with high detection accuracy. The strong actuation power and real-time sensory feedback from the composite hydrogels are expected to inspire novel flexible driving materials and intelligent sensing systems.

Enhancing Optical Properties of Zn-Mn Solid Solution Hybrid Halides for Wide Color Gamut Backlight Displays.

Hybrid metal halides display a range of optical properties and hold promise for various applications such as solid-state lighting, anti-counterfeiting measures, backlight displays, and X-ray detection. The incorporation of zinc into (C13H26N)2MnBr4 aims to enhance its structural rigidity and improve its narrow band green light emission properties. The resulting (C13H26N)2ZnBr4 compound exhibits an identical crystal structure to (C13H26N)2MnBr4, indicating the potential for a solid solution of varying Zn and Mn ratios within this structural framework. (C13H26N)2Zn0.2Mn0.8Br4 exhibits significantly enhanced properties, including a photoluminescence quantum yield of 92%, a minimum full width at half maximum of 43nm, and 85% retention of room temperature emission at 420K. Additionally, crystals of (C13H26N)2ZnCl4 and (C7H18N)2ZnX4 (X = Br, I) are synthesized, with (C7H18N)2ZnBr4 displaying luminescent color changes dependent on excitation. (C7H18N)2Zn0.2Mn0.8Br4 demonstrates reversible phase transitions and alterations in optical properties. A white light-emitting diode utilizing (C13H26N)2Zn0.2Mn0.8Br4 and commercial phosphors exhibited a color gamut of 112.2% of the National Television Standards Committee 1931 Standard. This investigation introduces a stable and highly efficient narrow-band green phosphor suitable for displays.

In situ observation of reversible phase transitions in Gd-doped ceria driven by electron beam irradiation

Ceria-based oxides are widely utilized in diverse energy-related applications, with attractive functionalities arising from a defective structure due to the formation of mobile oxygen vacancies (VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document}). Notwithstanding its significance, behaviors of the defective structure and VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} in response to external stimuli remain incompletely explored. Taking the Gd-doped ceria (Ce0.88Gd0.12O2-δ) as a model system and leveraging state-of-the-art transmission electron microscopy techniques, reversible phase transitions associated with massive VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} rearrangement are stimulated and visualized in situ with sub-Å resolution. Electron dose rate is identified as a pivotal factor in modulating the phase transition, and both the VO⋅⋅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{O}^{\\cdot \\cdot }$$\\end{document} concentration and the orientation of the newly formed phase can be altered via electron beam. Our results provide indispensable insights for understanding and refining the microscopic pathways of phase transition as well as defect engineering, and could be applied to other similar functional oxides.

Boosting the intrinsic kinetics of lithium vanadium phosphate via an electrochemically active cross-link framework

The monoclinic lithium vanadium phosphate Li3V2(PO4)3 (LVP) is considered a promising cathode for lithium-ion batteries (LIBs) due to its high working voltage (>4.0 V, vs. Li+/Li) and high theoretical specific capacity (197 mAh g−1). However, the electrochemical procedure accompanied by three-electron reactions in LVP has proven challenging due to the complexity or asymmetry of the reaction pathways, thus limiting its wide application. Herein, an electrochemically active cross-link framework of LVP, LiFe0.3Mn0.7PO4 (LFMP) and graphene are successfully synthesized by an in situ catalytic process, which enables stable cycling and high-rate capabilities up to 4.8 V (vs. Li+/Li). Graphene-like carbon can be formed in situ with VOx as the catalyst and polyvinyl alcohol as the carbon source, and LFMP also inhibits the growth of LVP particles, allowing rapid Li+ and electron transport in the cathodes. Both in situ and ex situ X-ray diffraction prove that the cross-link framework efficiently smooths the lattice mismatch and achieves highly reversible structural phase transitions. The prepared 0.9LVP·0.1LFMP is able to provide a superior rate capability of 123 mAh g−1 at 20 C. After 150 cycles, the 0.9LVP·0.1LFMP shows 97.4 % capacity retention even under a voltage of 4.8 V (vs. Li+/Li). This work develops a new strategy for the future design of high-voltage and high-power cathode materials for LIBs.

Revealing the role of B-site cations in the antiferroelectricity of NaNbO3-based perovskites

The promising prospects of antiferroelectric perovskite oxides in the realm of energy storage applications hinge on the unique field-induced phase transitions. Once the transition is triggered by the application of an electric field, characteristic double polarization loops appear. However, NaNbO3-based materials that exhibit a reversible phase transition are still rare, which hinders the practical applications of lead-free antiferroelectrics. Here, the impact of materials chemistry on the competition between antiferroelectric and ferroelectric states is demonstrated in a series of NaNbO3-based solid solutions with varying perovskite B-site cations, while the A-site is fixed as strontium. The crystal structure is analyzed on the basis of Rietveld refinement of high-energy X-ray diffraction data. The phase transition behavior as well as the antiferroelectric and ferroelectric properties are probed by a series of electrical measurements. The antiferroelectric phase is universally observed for all investigated materials in the virgin state. The SrTiO3-substituted system shows an irreversible phase transition similar to that of pure NaNbO3. In contrast, double polarization hysteresis loops are observed in the SrHfO3-, SrZrO3-, and SrSnO3-substituted systems. It is confirmed that compounds that can reduce the tolerance factor of the system contribute to the stabilization of the antiferroelectric order, while those that can reduce the electronegativity difference lead to more pronounced double loops. The competition between antiferroelectricity and ferroelectricity is linked to the competition between covalent and ionic bonding in perovskites.

Reversible Structural Phase Transitions in Zero-Dimensional Cu(I)-Based Metal Halides for Dynamically Tunable Emissions.

Exploring structural phase transitions and luminescence mechanisms in zero-dimensional (0D) metal halides poses significant challenges, that are crucial for unlocking the full potential of tunable optical properties and diversifying their functional capabilities. Herein, we have designed two inter-transformable 0D Cu(I)-based metal halides, namely (C19H18P)2CuI3 and (C19H18P)2Cu4I6, through distinct synthesis conditions utilizing identical reactants. Their optical properties and luminescence mechanisms were systematically elucidated by experiments combined with density functional theory calculations. The bright cyan-fluorescent (C19H18P)2CuI3 with high photoluminescence quantum yield (PLQY) of 77 % is attributed to the self-trapped exciton emission. Differently, the broad yellow-orange fluorescence of (C19H18P)2Cu4I6 displays a remarkable PLQY of 83 %. Its luminescence mechanism is mainly attributed to the combined effects of metal/halide-to-ligand charge transfer and cluster-centered charge transfer, which effects stem from the strong Cu-Cu bonding interactions in the (Cu4I6)2- clusters. Moreover, (C19H18P)2CuI3 and (C19H18P)2Cu4I6 exhibit reversible structural phase transitions. The elucidation of the phase transitions mechanism has paved the way for an unforgeable anti-counterfeiting system. This system dynamically shifts between cyan and yellow-orange fluorescence, triggered by the phase transitions, bolstering security and authenticity. This work enriches the luminescence theory of 0D metal halides, offering novel strategies for optical property modulation and fostering optical applications.

Elastin-like polypeptide-functionalized nanobody for column-free immunoaffinity purification of aflatoxin B1.

A column-free immunoaffinity purification (CFIP) technique for sample preparation of aflatoxin B1 (AFB1) was developed using an AFB1-specific nanobody (named G8) and an elastin-like polypeptide (ELP). The reversible phase transition between liquid and solid in response to temperature changes was exhibited by the ELP which was derived from human elastin. The G8 was tagged with ELPs of various lengths (20, 40, 60, and 80 repeat units) at the C-terminus using recursive directional ligation (RDL). Coding sequences were then subcloned into pET30a at the multiple cloning sites. Bioactive recombinant proteins were produced by expressing them as inclusion bodies in Escherichia coli BL21 (DE3), then dissolved and refolded. Analysis by indirect competitive enzyme-linked immunosorbent assay (icELISA) and transition temperature (Tt) measurement confirmed that the refolded G8-ELPs preserved the ability to recognize AFB1 as well as phase transition when the temperature rose above Tt. To establish the optimal conditions for cleaning AFB1, the effects of various parameters on recovery were investigated. The recovery in ELISA tests was 95 ± 3.67% under the optimized CFIP workflow. Furthermore, the CFIP-prepared samples were applied for high-performance liquid chromatography (HPLC) detection. The recovery in the CFIP-HPLC test ranged from 54 ± 1.86% to 98 ± 3.58% for maize, rice, soy sauce, and vegetable oil samples. To the best of our knowledge, this is the first report combining the function of both nanobody and ELP to develop a cleanup technique for small molecules in a complex matrix. The CFIP for the sample pretreatment was easy to use and inexpensive. In contrast to conventional immunosensitivity materials, the reagent utilized in the CFIP was entirely biosynthesized without any chemical coupling reactions. This suggests that the nanobody-ELP may serve as a useful dual-functional reagent for the development of sample cleaning or purification methods.

Thermodynamic investigation of reduced barium molybdates

Precise identification and thermodynamic assessment of the various phases in spent nuclear fuel are necessary for the accurate dynamic modeling of nuclear fuel. The Thermodynamics of Advanced Fuels – International Database (TAF-ID) compiles high-quality, self-consistent, and reliable thermodynamic data of various phases in chemical systems of interest for the international nuclear industry, such as the Ba-Mo-O ternary system. The thermodynamic properties of compounds in the Ba-Mo-O ternary system, especially those of hexavalent Mo, have been extensively studied and included in computational thermodynamic assessments. In contrast, compounds with Mo in reduced oxidation states, such as BaMo6O10 and Ba3Mo18O28, have been excluded from such assessments due to a lack of experimentally assessed thermodynamic data. In this work, high-quality samples of the aforementioned compounds were synthesized, and the first experimental assessment of their heat capacities in the temperature range 300–600 K were obtained. Furthermore, a reversible phase transition was identified at ∼380 K for BaMo6O10. The collected experimentally-assessed thermodynamic data from this work and initial calculated estimations of standard enthalpies of formation and entropies for these compounds were successfully integrated into a preliminary, updated Ba-Mo-O thermodynamic assessment using the CALPHAD method. Key thermodynamic properties of the newly included compounds (i.e., standard enthalpy of formation and entropy) were calculated using the new Ba-Mo-O assessment.

Low temperature phase transitions in the visible and near-infrared (VNIR) reflectance spectra of (NH4)2HPO4 and (NH4)HSO4 salts

The detection of ammonium bearing crystalline solids in salt-water systems on icy bodies and solar system bodies could provide information about the ascent of these salts from a deep reservoir within the hydrosphere. Due to their chemical-physical properties, NH4+ compounds play a key role both in the internal dynamics of celestial bodies and in the potential habitability of ocean worlds. In this work we analysed the reflectance spectra of two synthetic NH4+ salts: ammonium hydrogen phosphate (NH4)2HPO4 and ammonium hydrogen sulphate (NH4)HSO4 in the 1–4.2 μm spectral range at low temperature, between 110 and 290 K. For (NH4)2HPO4 we also examined the effect of three different grain sizes (150–125 μm; 125–80 μm; 80–32 μm). The collected reflectance spectra show absorption features related to NH4+ group overtone and combination modes in the 1–2.5 μm range. In particular, the bands located at ∼1.09 μm (3ν3), ∼1.30 μm (2ν3 + ν4), ∼1.58 μm (2ν3), ∼2.02 μm (ν2 + v3) and ∼ 2.2 μm (v3 + v4) could be useful to discriminate these salts. The low temperature spectra, compared to those at ambient temperature, reveal finer structures, displaying sharper and narrower absorption bands. The selected NH4+-bearing salts are subjected to reversible low temperature phase transitions, which are revealed in the spectra by a progressive growth and shift of the bands toward shorter wavelengths with a drastic change of their depth. We performed laboratory measurements of ammonium (NH4+) compounds to address the limited data available expanding the existing database. The collected cryogenic spectra can be directly compared with remote sensing data from planetary missions of the upcoming decade such as NASA's Europa Clipper, and ESA's JUICE and the newly launched James Webb Space Telescope expanding the existing database of ammonium compounds at cryogenic temperature.