Hexagonal Perovskite Research Articles

Novel Nb5+-doped hexagonal perovskite Ba5In2Al2ZrO13 (structure, hydration, electrical conductivity)

The new phase Ba5In2Al2Zr0.9Nb0.1O13.05 with hexagonal perovskite structure was obtained. The substitution of Zr4+ by smaller Nb5+ was accompanied by the incorporation of the oxygen interstitials and did not lead to a significant change in the lattice parameters. It was established that the investigated sample was capable for water incorporation from the gas phase, the hydration degree value was 0.24 mol H2O. IR-spectroscopy analysis defined the presence of OH−-groups with different thermal stability, which participate in different hydrogen bonds. The new phase Ba5In2Al2Zr0.9Nb0.1O13.05 demonstrates the predominant protonic conductivity at pH2O = 2·10−2 atm and Т600 °C.

Luminescence from Self‐Trapped Excitons and Energy Transfers in Vacancy‐Ordered Hexagonal Halide Perovskite Cs2HfF6 Doped with Rare Earths for Radiation Detection (Advanced Optical Materials 19/2022)

Cs2HfX6 halides show a vacancy-ordered cubic double perovskite structure when X = Cl, Br, and I. As to the first member of the halide family, Zhiping Luo and co-workers (article number 2201374) identify Cs2HfF6 as a new type of vacancy-ordered hexagonal perovskite. It is composed of single layers of building blocks. Tunable emission is obtained based on self-trapped exciton emissions from the host and energy transfers in the rare-earth-doped material. From energy-dependent cathodoluminescence and time-resolved X-ray radioluminescence, the co-doped material is found to be more sensitive to radiation energy than the singly-doped or pristine host.

Ecofriendly High NIR Reflectance Ceramic Pigments Based on Rare Earths Compared with Classical Chromophores Prepared by DPC Method

A high NIR reflectance ceramic pigments palette based on rare earths except black (La,Li-SrCuSi4O10 blue wesselsite, Pr-CeO2 red-brown cerianite, Mo-Y2Ce2O7 yellow cerate, Sr4Mn2CuO9 black hexagonal perovskite) was compared with the coolest traditional pigments palette prepared by dry powder coating (DPC) to obtain “core-shell” pigments (Co-willemite blue, Cr-franklinite brown, Ni,Sb-rutile yellow, Co,Cr-spinel black). Adding CaCO3 as a binder, normalized NIR reflectance at L* = 85, 55 and 30 was compared for yellow, brown and blue-black powders, respectively. Rare earths lack intense absorption bands in the NIR range and therefore its pigments show higher NIR reflectance, but normalized measurements show smaller differences and even have an inverse result for blue pigments. The pigmenting capacity and stability study in different media show that the stability of cool rare earth pigments is lower than that of DPC classical pigments, except in the case of the red-brown Pr-cerianite pigment.

BaCoO3−δ perovskite-type oxygen carrier for chemical looping air separation, part Ⅰ: Determination of oxygen non-stoichiometry and cyclic stability of oxygen carrier

Chemical looping air separation (CLAS) is a cost-effective high-temperature air separation technology, and finding suitable oxygen carriers with high oxygen selectivity and capacity is of vital importance to it. Perovskite-type oxides have been extensively studied as oxygen carriers due to their high oxygen selectivity. In this work, BaCoO3-δ perovskite oxide with large oxygen capacity was proposed as an excellent oxygen carrier for CLAS. BaCoO3-δ perovskite powder was synthesized through a sol–gel method, and the determination of oxygen non-stoichiometry and cyclic stability of BaCoO3-δ was investigated via thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Results indicated that the oxygen non-stoichiometry of BaCoO3-δ was a function of temperature and oxygen partial pressure, and the empirical formula was determined by linear fitting in the range of δ less than 0.5. The standard enthalpy change and standard entropy change of the oxygen desorption reaction were 169.43 kJ/mol and 156.19 kJ/(mol·K) at δ of 0.38, which increased to 292.58 kJ/mol and 298.81 kJ/(mol·K) at δ of 0.47, respectively. The oxygen desorption amount and desorption rate of BaCoO3-δ remained extremely stable during 50 cycles at 875℃, with an oxygen capacity of approximately 0.018 g O2/g BaCoO3 of each cycle. The kinetics of the oxygen desorption process of BaCoO3-δ perovskite was described using the 3-D diffusion Jander model, and the obtained values of apparent activation energy (Ea) and pre-exponential factor (A) were 209.79 kJ/mol and 1.93E06, respectively. Further results indicated that BaCoO3-δ demonstrated a hexagonal perovskite phase, the desorbed oxygen was provided by lattice oxygen in perovskite, the crystal structure remained stable during cycles, and the micro-morphology slightly changed after 50 cycles.

Characteristics of electrolyte-supported SOFC single cells using hexagonal perovskite Ba3MoNbO8.5 and Ba7Nb4MoO20 ceramics

The characteristics of two solid oxide fuel cells (SOFCs) were compared using Ba3MoNbO8.5 and Ba7Nb4MoO20 sintered at 1100 and 1300 °C, respectively, as electrolytes. The electrolyte-supported SOFC single cells, Pt ǀ Sm0.2Ce0.8O1.9 ǀ electrolyte ǀ Sm0.2Ce0.8O1.9 ǀ Pt, with an electrolyte thickness of 1.0 mm were prepared. The resistivity of the bulk + grain boundary components of Ba3MoNbO8.5 and Ba7Nb4MoO20 were 2.25k and 212 Ω cm, respectively, at 600 °C, and their apparent activation energies for ion conduction were 122.3 and 72.8 kJ mol−1, respectively at 450–600 °C. When the I–V curves were evaluated at 450–600 °C with the introduction of 3% H2 (N2 balance) and air to the anode and cathode, respectively, the open circuit voltages and maximum power outputs at 600 °C were 0.95 V and 1.3 mW cm−2 for Ba3MoNbO8.5 and 0.97 V and 9.3 mW cm−2 for Ba7Nb4MoO20, respectively.

Hybrid Organic–Inorganic Halide Derivatives of the 2H Hexagonal Perovskite Structure

Hybrid Organic–Inorganic Halide Derivatives of the 2H Hexagonal Perovskite Structure

Effect of Zr and Hf addition on microstructure and tensile properties of high-Al Ni-based ODS superalloys

In this paper, three kinds of high-Al Ni-based oxide dispersion strengthening (ODS) superalloys, ODS-Z (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.6Zr, wt.%), ODS-H (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.8Hf) and ODS-ZH (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.6Zr–0.8Hf), were prepared by mechanical alloying (MA) and hot isotropic pressing (HIP). The effect of Zr and Hf addition on grains, oxides, γ′ phases and mechanical properties of Ni-based ODS superalloys was investigated. The result exhibited that grain size is refined by Hf addition. The addition of Zr or Hf significantly varies the type and distribution of oxides. The mean size and number density of oxides are 11.8 nm and 6.64 × 1021 m−3 for ODS-Z, 9.5 nm and 7.86 × 1021 m−3 for ODS-H, 10.7 nm and 7.53 × 1021 m−3 for ODS-ZH, respectively. The oxides formed in ODS-Z are hexagonal δ-Y4Zr3O12 and YAlO3 perovskite (YAP). The oxides in ODS-H consist of cubic-structure Y2Hf2O7, YAP and monoclinic Y4Al2O9 (YAM). However, only Y2Hf2O7 and Y4Zr3O12 are observed in ODS-ZH. The addition of Zr and Hf does not change average size and volume fraction of γ′ phases. Compared with the addition of Zr or Hf alone, the co-addition of Zr and Hf exhibits high tensile strength while improves significantly ductile at room temperature and 700 °C.

Luminescence from Self‐Trapped Excitons and Energy Transfers in Vacancy‐Ordered Hexagonal Halide Perovskite Cs2HfF6 Doped with Rare Earths for Radiation Detection

AbstractCompared to halides Cs2HfX6 (X = Cl, Br, I) with a vacancy‐ordered cubic double perovskite structure, the halide Cs2HfF6 (CHF), with a hexagonal Bravais lattice, possesses a higher mass density and chemical stability for radiation detection. Luminescence properties and energy transfer mechanisms of rare‐earths‐doped CHF materials are studied here. The structure of CHF is identified as a new type of vacancy‐ordered hexagonal perovskite, with the same type of building blocks of the double perovskite but stacked with single layers. Density‐functional theory calculations reveal a large bandgap of CHF. A broad emission is observed from the pristine CHF host, which is suggested to be associated with self‐trapped excitons (STEs). A series of rare‐earths‐doped materials are designed utilizing the STE emissions, and efficient energy transfers from STEs and Tb3+ to Eu3+ are achieved for tunable emissions. The codoped material shows stable emission under X‐ray irradiation, with 10.2% reduction from its initial emission intensity, associated with possible structural evolution by radiation‐induced deformation of the soft host. The radiation responses of singly and codoped materials are evaluated, and the codoped material is found to be more sensitive to the radiation energy than the singly doped or pristine CHF for radiation detection.

Localized Spin Dimers and Structural Distortions in the Hexagonal Perovskite Ba3CaMo2O9.

Extended solid-state materials based on the hexagonal perovskite framework are typified by close competition between localized magnetic interactions and quasi-molecular electronic states. Here, we report the structural and magnetic properties of the new six-layer hexagonal perovskite Ba3CaMo2O9. Neutron diffraction experiments, combined with magnetic susceptibility measurements, show that the Mo2O9 dimers retain localized character down to 5 K and adopt nonmagnetic spin-singlet ground states. This is in contrast to the recently reported Ba3SrMo2O9 analogue, in which the Mo2O9 dimers spontaneously separate into a mixture of localized and quasi-molecular ground states. Structural distortions in both Ba3CaMo2O9 and Ba3SrMo2O9 have been studied with the aid of distortion mode analyses to elucidate the coupling between the crystal lattice and electronic interactions in 6H Mo5+ hexagonal perovskites.

Iridium‐Doped 10H‐Phase Perovskite BaCo0.8Fe0.15Ir0.05O3–δ as an Efficient Oxygen Evolution Reaction Catalyst

Comprehensive SummaryDesigning low‐cost and high‐performance catalysts of electrocatalytic oxygen evolution reaction (OER) has always been one of the hot topics in current research. Hexagonal perovskite materials show great application potential in this field. Here, we synthesized 5% Iridium (Ir)‐doped hexagonal phase perovskite BaCo0.8Fe0.15Ir0.05O3–δ (BCFI). Using the Rietveld method to refine the structure, combining with the spherical aberration corrected high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) atomic imaging, we found that BCFI is a ten‐layer hexagonal (10H) structure, which belongs to the Pm2 space group. In addition, BCFI shows excellent OER catalytic effect and good stability in 1 mol/L KOH solution, and the overpotential reaches 294 mV at a current density of 10 mA cm–2. The reduction of Cobalt (Co) valence state induced by Ir doping significantly enhances the OER activity of BCFI. Meanwhile, density functional theory (DFT) calculations show that the 2p‐band center of oxygen (O) in BCFI is closer to the Fermi level than that in undoped BaCo0.8Fe0.2O3‐δ (BCF), which is beneficial to the OER. This work reveals a novel 10H‐BCFI material with excellent OER performance, and provides a basis for the design of hexagonal perovskite materials in OER and other energy conversion fields.

(Digital Presentation) The New 2H Hexagonal Double Perovskite Ba2CoMnO6 As a Superior OER Catalyst in Alkaline Media

Climate change has stimulated great interest in developing clean and renewable energy conversion and storage solutions. Emerging technologies for solutions, like unitized regenerative fuel cells, metal-air batteries, and water electrolyzers, depend on the reliable catalyst materials suited for long-term application in alkaline environments[1]. In particular, the demanding reaction in these systems is the oxygen evolution reaction involving complex multielectron/proton transfer processes and thus sluggish kinetic.[2] At present, the state-of-the-art OER catalysts are IrO2 and RuO2. However, the high cost and scarcity of these materials severely prevent the wide-scale application of these systems.[3] Perovskite oxide (e.g., single perovskite expressed as ABO3) electrocatalysts are particularly considered next-generation OER catalysts due to their adjustable physicochemical properties and, as a consequence, their catalytic properties by substitution of ions in the A and B sites.[4] Via doping both at A and B site, double perovskite oxides structure can form (AA′B2O5+δ), which were shown to have stable structure during the OER due to proper O p-band center position relative to the Fermi level. The previous research shows that hexagonal perovskites exhibit enhanced catalytic activity rather than cubic or tetragonal perovskites, which is associated with the face-sharing octahedral unit. [5,6] In this work, we systematically investigate doping of parent La2CoMnO6 with Ba to tune the crystal structure and electronic structure. A series of the double perovskites with the chemical formula of La2-xBaxCoMnO6 (x = 0, 0.5, 1.5, 2) were fabricated via the modified Sol-Gel Pechini method. According to Goldschmidt tolerance factor, it is expected that when Ba amount increases in the A site, the crystal structure changes from cubic to hexagonal, which can contribute to electrocatalytic OER activity based above discussions. Furthermore, it is anticipated that increasing Ba content at the A site should result in higher valence state of transition metals due to stabilizing charge balance of the structure. It is widely reported that presence of higher valence state of transition metals is beneficial for OER.The crystal structure was confirmed by combining powder X-ray diffraction (XRD) patterns and selected area electron diffraction (SAED) patterns. The two-layer hexagonal structure of Ba2CoMnO6 (BCM) was further characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The results show doping of Ba into parent La2CoMnO6 resulted in the hexagonal phase formation and BCM achieves a current density of 10 mA cm–2 at a low overpotential of 288 mV and has the highest intrinsic activity in the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2). Furthermore, BCM exhibits outstanding stability of 12 h in a 0.1 M KOH electrolyte. The electronic structure and surface work function values of the catalysts were examined with X-ray photoelectron spectroscopy (XPS). XPS analysis revealed that valence state of Co and Mn increases through Ba amount in the structure, indicating the double perovskite oxide charge balance is maintained. In addition to valence state analysis, we performed work function analysis of the catalysts tested in this work. The result shows work function of the series of BaxLa2-xCoMnO6 (x = 0, 0.5, 1, 1.5, 2) substantially decreases with Ba content. Here, we show that the high intrinsic activity of BCM is not only related with the hexagonal structure and also may be related with exhibiting lower work function value in the series. In addition, our approach presents a new strategy, air quenching method, to synthesize a phase pure 2H-hexagonal double perovskite oxide. [1] Y. Zhou, X. Guan, H. Zhou, K. Ramadoss, S. Adam, H. Liu, S. Lee, H. Shi, M. Tsuchiya, D. Fong and S. Ramanathan, Nature, 534, 231-234 (2016).[2] X. Cui, P. Ren, D. Deng, J. Deng and X. Bao, Energy & Environmental Science, 9, 123-129 (2016).[3] X. Qiu, Y. Zhang, Y. Zhu, C. Long, L. Su, S. Liu and Z. Tang, Advanced Materials, 33, 2001731 (2020).[4] W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li and Y. Yan, Energy & Environmental Science, 12, 442-462 (2019).[5] L. Tang, W. Zhang, D. Lin, Y. Ren, H. Zheng, Q. Luo, L. Wei, H. Liu, J. Chen and K. Tang, Inorganic Chemistry Frontiers, 7, 4488-4497 (2020).[6] C. Chen, G. King, R. M. Dickerson, P. A. Papin, S. Gupta, W. R. Kellogg and G. Wu, Nano Energy, 13, 423-432 (2015).

BaFe0.875Re0.125O3−δ and BaFe0.75Ta0.25O3−δ as potential cathodes for solid-oxide fuel-cells: a structural study from neutron diffraction data

Abstract In this work, two new perovskites of composition BaFe0.875Re0.125O3−δ and BaFe0.75Ta0.25O3−δ , designed from ab-initio calculations to fulfill different requisites of cathode materials for solid-oxide fuel cells (SOFC), were prepared and studied from the structural point of view from neutron powder diffraction (NPD) data. They are both derivatives of BaFeO3 hexagonal perovskite (space group P6 3 /mmc), typified as the 6H polytype, stabilized when the perovskite tolerance factor slightly overpasses the unity. Whereas BaFe0.875Re0.125O3−δ keeps this structural type, as demonstrated in this crystallographic study from NPD data at 295 and 4 K, with unit-cell parameters a = 5.70177(7); c = 14.0334(2) Å at 295 K, the second material, BaFe0.75Ta0.25O3−δ , is cubic and can be defined in the Pm-3m space group, corresponding of the perovskite arystotype, with a = 4.05876(3) Å. A conspicuous oxygen deficiency is observed, with a refined stoichiometry of 2.86(3) per formula unit. The anisotropic displacement factors for oxygen atoms in this last material are flattened disks perpendicular to the (Fe,Ta)-O-(Fe,Ta) direction, suggesting a dynamic tilting of the octahedra that could be related to the oxygen motion via oxygen vacancies across the structure. This is a pre-requisite for functional mixed-ionic-electronic (MIEC) materials performing as cathodes in SOFC.

A novel low-loss Ba12SbNb9O36 microwave dielectric ceramic with 18-layer hexagonal perovskite structure

A novel low-loss Ba12SbNb9O36 microwave dielectric ceramic is synthesized via the solid-state reaction method. TG-DSC thermal analysis is employed to study the phase formation process of the samples. The XRD and TEM analyses reveal that the ceramic samples all confirmed a hexagonal perovskite structure with the R-3 m space group. The refinement result shows that the ceramic is a shifted hexagonal perovskite with an 18-layer structure. Porosity has an important impact on permittivity and dielectric loss in this ceramic. Raman spectroscopy revealed that the quality factor shows a close connection with the FWHM of the A1g mode at 777 cm−1. XPS analysis shows that the oxidation of Sb ions deteriorates the τf value of the ceramic. The optimum microwave dielectric properties (εr = 35.59, Q × f = 58,297 GHz and τf = +34.14 ppm/°C) are obtained by sintering at 1250 °C, making the Ba12SbNb9O36 ceramic a promising candidate for high-performance microwave applications.

Synthesis, structural and physical properties of ABO3 based hexagonal polytypes: A review and discussion

The aim of this review paper is to provide the compact overview of experimental synthesis route, crystallography of perovskite (ABO3) hexagonal polytypes and their related physical properties. Structural stacking sequence of the oxygen deficient hexagonal perovskite oxides (ABO3-δ) is briefly discussed. The fundamental aspects of magnetic and electrical properties involved in hexagonal polytypes are elaborated using reported systems. The magnetic field induced effect such as magnetocaloric effect, magnetoresistance and magneto-dielectric effect in perovskite hexagonal polytypes are also discussed for their possible application in magnetic refrigeration, magnetic sensors and memory devices.

Proton and Oxygen-Ion Conductivities of Hexagonal Perovskite Ba5In2Al2ZrO13.

The hexagonal perovskite Ba5In2Al2ZrO13 and In3+-doped phase Ba5In2.1Al2Zr0.9O12.95 were prepared by the solid-state synthesis method. The introduction of indium in the Zr-sublattice was accompanied by an increase in the unit cell parameters: a = 5.967 Å, c = 24.006 Å vs. a = 5.970 Å, c = 24.011 Å for doped phase (space group of P63/mmc). Both phases were capable of incorporating water from the gas phase. The ability of water incorporation was due to the presence of oxygen deficient blocks in the structure, and due to the introduction of oxygen vacancies during doping. According to thermogravimetric (TG) measurements the compositions of the hydrated samples corresponded to Ba5In2Al2ZrO12.7(OH)0.6 and Ba5In2.1Al2Zr0.9O12.54(OH)0.82. The presence of different types of OH−-groups in the structure, which participate in different hydrogen bonds, was confirmed by infrared (IR) investigations. The measurements of bulk conductivity by the impedance spectroscopy method showed that In3+-doping led to an increase in conductivity by 0.5 order of magnitude in wet air (pH2O = 1.92·10−2 atm); in this case, the activation energies decreased from 0.27 to 0.19 eV. The conductivity−pO2 measurements showed that both the phases were dominant proton conductors at T < 500 °C in wet conditions. The composition Ba5In2.1Al2Zr0.9O12.95 exhibited a proton conductivity ~10−4 S·cm−1 at 500 °C. The analysis of partial (O2−, H+, h•) conductivities of the investigated phases has been carried out. Both phases in dry air (pH2O = 3.5·10−5 atm) showed a mixed (oxygen-ion and hole) type of conductivity. The obtained results indicated that the investigated phases of Ba5In2Al2ZrO13 and Ba5In2.1Al2Zr0.9O12.95 might be promising proton-conducting oxides in the future applications in electrochemical devices, such as solid oxide fuel cells. Further modification of the composition and search for the optimal dopant concentrations can improve the H+-conductivity.

Air‐Stabilized Lead‐Free Hexagonal Cs3Bi2I9 Nanocrystals for Ultrahigh‐Performance Optical Detection

AbstractBroadband photodetectors possess enormous potentials for diverse applications while it is generally subjected to a lack of active materials with high performances under user‐friendly conditions. Bismuth‐based perovskites are promising and demonstrate better air stability than lead halide perovskites against moisture, heat, and light. In the present work, lead‐free all‐inorganic hexagonal Cs3Bi2I9 perovskite nanocrystals are successfully fabricated via a modulated colloidal synthetic route. The Cs3Bi2I9 nanocrystals are monodispersed with a size of ≈28 nm, which are applied for the construction of flexible Cs3Bi2I9 detector and vertical heterogeneous structured photodetector of p‐Si/Cs3Bi2I9/graphene. The flexible detector not only demonstrates excellent detective performance, but also yields high‐resolution photographs as an imaging sensor. The p‐Si/Cs3Bi2I9/graphene photodetector exhibits broad spectral response from ultraviolet to infrared light (254−1064 nm) with microsecond response time (31/34 µs). In particular, it performs with a high responsivity of 23.6 A W−1 and a high specific detectivity of 1.75 × 1013 Jones under 650 nm illumination even in weak light intensity as low as 1 µW cm−2, and exhibits excellent stability in ambient air, which is obviously ahead of the previously reported work. In addition, finite element analysis further demonstrates the excellent optoelectronic properties of Cs3Bi2I9 materials and the broad spectral response of vertical heterojunctions.

First principles study on optical and thermal properties of BaTiS3

Electronic, optical and thermal properties of hexagonal perovskite structure of BaTiS3, are studied, by means of the density functional theory (DFT) implemented on CASTEP, Material Studio, computer program. The data is optimized with generalized gradient approximation (GGA) and exchange correlation function called local density approximation (LDA), within the Broyden-Goldfarb-Shanno (BFGS) scheme of minimization and Koelling-Harmon relativistic treatment. Structure of BaTiS3, which we studied, crystallizes in the space group P63/mmc. Our results for structural, electronic and thermal properties of BaTiS3 are reported for the first time in comparison with experimental and other theoretical results wherever these are available. The electronic band structure reveals p-type semiconducting behavior and major contribution occurs from S-3p orbitals in Valence band and the conduction band is basically constructed from Ti-3d states. Reflectivity of BaTiS3 is also founded to be higher within visible and in ultraviolet region up to 25 eV, which indicates the potentiality of this material to be utilized as a jacket to elude solar heating. Coefficient of absorption spectra of BaTiS3 reveals the conducting nature of this material. The negative values of ε1(ω) is additionally observed,which is obvious indication of Drude like behavior seen in metals. Index of refraction is relatively higher within the infrared section and steadily lowered within the visible and ultraviolet frequency region. Analysis for conductivity also favors the photoconductivity with small photon energy. Thermo dynamical properties reported for the first time with Debye temperature of 1000 K.

First-principles thermochemical properties of hexagonal and cubic phase BaMnO3

BaMnO3 perovskite oxide is an interesting material for many high-temperature technological applications due to its facile reduction capacity at reasonably low temperature. The thermochemical properties of BaMnO3 largely determine this reduction behaviour at high temperature. However, the temperature-dependent thermochemical properties of hexagonal and cubic BaMnO3 remain uncharacterized. Herein the structural and thermochemical properties (entropy, specific heat and relative molar enthalpy) of hexagonal and cubic BaMnO3 perovskites are predicted using first principles calculations. Their corresponding phonon dispersions and vibrational density of states are illustrated to show the individual atomic contributions to their thermochemical properties. It is demonstrated that the choice of generalized gradient approximation DFT functional does not appreciably influence the structural or thermochemical properties. Data AvailabilityThe raw data required to reproduce these findings are available from the authors upon reasonable request.

A high sensitivity dual-mode optical thermometry based on charge compensation in ZnTiO3:M (M = Eu3+, Mn4+) hexagonal prisms

Optical thermometer based on dual-mode fluorescence intensity ratiometric thermometry has been attracted more attention due to its higher sensitivity. In order to obtain optical thermal probe with high sensitivity, ZnTiO3 hexagonal prisms with hexagonal perovskite structure were fabricated by using self-assembly method, and Al3+ ions were introduced into the crystal lattices of ZnTiO3 doped with Eu3+/Mn4+ to improve the optical properties. The emission intensity assigned to Eu3+ was enhanced about twice with the charge compensation of Al3+ between Eu3+ and Ti3+. While the luminescence ratio between the thermal coupled level of Eu3+ revealed poor temperature dependence property. The emission assigned to 2Eg→4A2g (713 nm) transition of Mn4+ revealed an huge thermal quenching. Using the luminescence ratio between 5D0→7F2 (5D0→7F1) transition of Eu3+ to 2Eg→4A2g of Mn4+, the higher relative sensitivity of 2.7 %K-1was obtained. The charge compensation of Al3+ improved the coordination and reduced the relative sensitivity, Sr =1.85 %K−1. The results suggested the potential application in optical temperature probes for ZnTiO3: Mn4+,Eu3+ phosphor.

Silver(I)-Based Molecular Perovskite Energetic Compounds with Exceptional Thermal Stability and Energetic Performance.

In recent years, molecular perovskite energetic materials have attracted more attention because of their simple synthesis processes, high thermal stabilities, excellent performances, and great significance as a design platform for energetic materials. To explore the possibility of the application of molecular perovskite energetic materials in heat-resistant explosives, four silver(I)-based molecular perovskite energetic compounds, (H2A)[Ag(ClO4)3], where H2A = piperazine-1,4-diium (H2pz2+) for PAP-5, 1-methyl-piperazine-1,4-diium (H2mpz2+) for PAP-M5, homopiperazine-1,4-diium (H2hpz2+) for PAP-H5, and 1,4-diazabicyclo[2.2.2]octane-1,4-diium (H2dabco2+) for DAP-5, were synthesized by a one-pot self-assembly strategy and structurally characterized. The single-crystal structures indicated that PAP-5, PAP-M5, and DAP-5 possess cubic perovskite structures while PAP-H5 possesses a hexagonal perovskite structure. Differential thermal analyses showed that their onset decomposition temperatures are >308.3 °C. For PAP-5 and DAP-5, they have not only exceptional calculated detonation parameters (D values of 8.961 and 8.534 km s-1 and P values of 42.4 and 37.9 GPa, respectively) but also the proper mechanical sensitivity (impact sensitivities of ≤10 J for PAP-5 and 3 J for DAP-5 and friction sensitivities of ≤5N for both PAP-5 and DAP-5) and thus are of interest as potential heat-resistant primary explosive components.