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Multicomponent flux systems based on both Li2WO4-B2O3-Li2O-CuO-Cr2O3 and Bi2O3-MoO3-B2O3-Na2O-CuO-Cr2O3 were studied in order to grow Cu2CrBO5 crystals. The conditions for Cu2CrBO5 crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr2O3 solubility. Phase boundaries between CuCrO2, Cu2CrO4, and Cu2CrBO5 were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu2CrBO5 grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr2+ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu2CrBO5. The anomaly at TC ≈ 42 K and the antiferromagnetic phase transition at TN ≈ 119 K were considered. Polarized Raman spectra of Cu2CrBO5 were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature TN ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu2CrBO5 is discussed. [ABSTRACT FROM AUTHOR]

Phosphors that exhibit tunable broadband emissions are highly desired in multi-functional LEDs, including pc-WLEDs and pc-NIR LEDs. In this work, broadband emissions were obtained and modulated in the unexpectedly wide spectral range of 517–609 nm for (Lu0.99−xGdxBi0.01)2WO6 phosphors by tuning the Gd3+ content (x = 0–0.99). The effects of Gd3+ doping on phase constituents, particle morphology, crystal structure, and photoluminescence were systematically investigated. Broadband green emission was obtained from Gd3+-free (Lu0.99Bi0.01)2WO6 phosphors (x = 0), whose emission intensity was enhanced by 50% with 5 at% Gd3+ (x = 0.05). The phase transition happened when x > 0.50 and the broadband red-NIR emission was obtained when x = 0.75–0.99. Three luminescence centers were proved to be responsible for the broadband green emissions via crystal structure, spectral fitting and fluorescence decay analysis. A pc-WLED with a high color rendering index (Ra = 91.3), a stable emission color, and a low color temperature (3951 K) was fabricated from the (Lu0.94Gd0.05Bi0.01)2WO6 broadband green phosphor, and an LED device that simultaneously emits high color rendering index white light and NIR light was obtained with the (Gd0.99Bi0.01)2WO6 broadband red-NIR phosphor. Night vision and noninvasive imaging were also demonstrated using the latter LED device. [ABSTRACT FROM AUTHOR]

Zero‐dimensional (0D) metal halides have drawn increasing attention due to the attractive structure dependent photoluminescence (PL) properties. Here, we report two new 0D organic–inorganic hybrid Sb‐based halides, (MTP)6SbBr6Sb2Br9⋅H2O (MTP=Methyltriphenylphosphonium, crystal 1) and (MTP)2SbBr5 (crystal 2), featuring a reversible structural phase transformation and tunable orange and red emissions upon dehydration and rehydration of H2O molecules. Intriguingly, a subsequent heat treatment further enables the formation of glassy state (MTP)2SbBr5 (glass 3) with near‐infrared luminescence, moreover, a sequential reverse phase transformation from glass 3 to crystal 2 and 1 is triggered by acetonitrile and water vapor stepwise. The anti‐counterfeiting demo based on the tunable and reversible PL switching is finally achieved and thus the phase structure engineering in 0D metal halides expands their multiple applications in optical fields. [ABSTRACT FROM AUTHOR]

The detection of amide solvents is essential to human health due to their carcinogenicity. A simple, solvatochromic luminescent material is presented for quick and accurate detection of amides. The luminescence color variation from blue to yellow is ascribed to the amide-induced phase transformation from Cs2ZnBr4:Cu to CsBr:Cu+/Cu2+. [ABSTRACT FROM AUTHOR]

The development of lead‐free perovskite photoelectric materials has been an extensive focus in the recent years. Herein, a novel one‐dimensional (1D) lead‐free CsMnCl3(H2O)2 single crystal is reported with solvatochromic photoluminescence properties. Interestingly, after contact with N,N‐dimethylacetamide (DMAC) or N,N‐dimethylformamide (DMF), the crystal structure can transform from 1D CsMnCl3(H2O)2 to 0D Cs3MnCl5 and finally transform into 0D Cs2MnCl4(H2O)2. The solvent‐induced crystal‐to‐crystal phase transformations are accompanied by loss and regaining of water of crystallization, leading to the change of the coordination number of Mn2+. Correspondingly, the luminescence changes from red to bright green and finally back to red emission. By fabricating a test‐paper containing CsMnCl3(H2O)2, DMAC and DMF can be detected quickly with a response time of less than one minute. These results can expand potential applications for low‐dimensional lead‐free perovskites. [ABSTRACT FROM AUTHOR]

A study of heat capacity, thermal dilatation, susceptibility to hydrostatic pressure, permittivity and polarization loops was carried out on NH4HSO4-porous glass nanocomposites (AHS + PG) as well as empty glass matrices. The formation of dendrite clusters of AHS with a size, dcryst, exceeding the pore size was found. An insignificant anisotropy of thermal expansion of AHS + PG showing statistically uniform distribution of AHS with random orientations of nanocrystallites over the matrix was observed. The effect of internal and external pressures on thermal properties and permittivity was studied. At the phase transition P-1 ↔ Pc, a strongly nonlinear decrease in the entropy ΔS2 and volume strain (ΔV/V)T2 was observed with decreasing dcryst. The linear change in temperatures of both phase transitions P-1 ↔ Pc ↔ P21/c under hydrostatic pressure is accompanied by the expansion of the temperature range of existence of the ferroelectric phase Pc, while this interval narrows as dcryst decreases. [ABSTRACT FROM AUTHOR]

A facile and controllable ethanol/water aided hydrothermal process was developed to prepare the NaCaSiO3OH:Tb3+/Eu3+ phosphor. The morphologies were in situ constructed with the phase transformation from NaCaSiO3OH to Na2Ca2Si2O7, and the intrinsic crystal structural transformation mechanism and the dependence of their photoluminescence tuning on the Tb3+/Eu3+ ratio have been discussed. [ABSTRACT FROM AUTHOR]

A case of phosphor is reported where the cooling rate parameter significantly influences the luminescence property. By quenching the sample after the high-temperature solid-state reaction at 1250°C, we successfully prepared the Eu2+-doped α form Ca3( PO4)2 (α- TCP:Eu2+) as a new kind of bright cyan-emitting phosphor. The unusual emission color variation (from cyan to blue) depends on the cooling rate after sintering and Eu2+ doping level as it was observed in the TCP-based phosphors. By the Rietveld analysis, it is revealed that the cyan- and blue-emitting phosphors are two different TCP forms crystallizing in the monoclinic (space group P21/ a, α- TCP) and the rhombohedral structure (space group R3 c, β- TCP), respectively. Upon 365 nm UV light excitation, α- TCP:Eu2+ exhibits an asymmetric broad-band cyan emission peaking at 480 nm, while β- TCP:Eu2+ displays a relatively narrow-band blue emission peaking at 416 nm. The Eu2+-doping in Ca3( PO4)2 shifts the upper temperature limit of the stable structural range of β form from 1125°C to ≥1250°C. Moreover, the crystal structures of α/β- TCP:Eu2+ were compared in the aspects of compactness and cation site sets. The emission thermal stability of α/β- TCP:Eu2+ was comparatively characterized and the difference was related to the specific host structural features. [ABSTRACT FROM AUTHOR]

Abstract: X-ray and heat capacity measurements were performed on Rb2KMoO3F3 and Rb2KWO3F3 single crystals. A significant difference in the thermal parameters of atoms in 4a and 8c sites of Fm-3m structure was found, which depended on the central atom. Calorimetric measurements have revealed the heat capacity anomalies at 195 and 67 K, respectively, in Rb2KMoO3F3 and Rb2KWO3F3. The standard molar enthalpy and entropy were determined. Entropy changes associated with phase transitions in oxyfluorides under study and related Rb2KTiOF5 are discussed. [Copyright &y& Elsevier]

Berichtigung: Solvatochromic Photoluminescent Effects in All-Inorganic Manganese(II)-Based Perovskites by Highly Selective Solvent-Induced Crystal-to-Crystal Phase Transformations Lead-free materials, luminescence, manganese, phase transitions, low-dimensional perovskites Keywords: lead-free materials; low-dimensional perovskites; luminescence; manganese; phase transitions EN lead-free materials low-dimensional perovskites luminescence manganese phase transitions 25387 25387 1 11/17/21 20211122 NES 211122 In this Research Article one of the affiliations for the authors Prof. Ziyong Cheng and Prof. Jun Lin was inadvertently omitted. [Extracted from the article]

Keywords: lead-free materials; low-dimensional perovskites; luminescence; manganese; phase transitions EN lead-free materials low-dimensional perovskites luminescence manganese phase transitions 25183 25183 1 11/17/21 20211122 NES 211122 In this Research Article one of the affiliations for the authors Prof. Ziyong Cheng and Prof. Jun Lin was inadvertently omitted. Corrigendum: Solvatochromic Photoluminescent Effects in All-Inorganic Manganese(II)-Based Perovskites by Highly Selective Solvent-Induced Crystal-to-Crystal Phase Transformations Manganese, phase transitions, luminescence, lead-free materials, low-dimensional perovskites. [Extracted from the article]

[Display omitted] • Second order phase transition Cmcm ↔ P 2 1 / m at 200 K is far from the tricritical point. • All structural elements are ordered in both phases. • Structure distortions are associated with the rotation of CdF 7 and ZrF 7 bipyramids. • A small change in entropy and high sensitivity to hydrostatic pressure was detected. X-ray, calorimetric and dilatometric studies of RbCdZrF 7 revealed the existence of the second order phase transition Cmcm ↔ P 2 1 / m at T 0 = 200 K. The structure of the initial and distorted phases is ordered. The phase transition is associated with displacements of fluorine atoms, which leads to minor rotations of the CdF 7 and ZrF 7 pentagonal bipyramids. A small change in entropy, 0.1 R , is characteristic of displacive-type transformations. An anomalously high susceptibility of the transition temperature to hydrostatic pressure was found. [ABSTRACT FROM AUTHOR]

• Structural change, heat capacity and thermal expansion of fluoride K 3 ZrF 7 are studied. • Structural distortions are mainly associated with the rotation of the ZrF 7 3− bipyramid. • Intriguing behavior of thermal properties was observed in the low temperatures phase. • The results obtained are useful for correcting the model of structural disordering. X-ray, calorimetric and dilatometric studies of K 3 ZrF 7 revealed the existence of the phase transition Fm- 3 m ↔ R- 3 m at T 0 = 320 K. The structural model assumes a disorder of a pentagonal bipyramid ZrF 7 with the following ratio of equivalent orientation positions in the initial and distorted phases: 12 to 6. A good agreement was found between the experimental and model-calculated changes in strain and entropy during the phase transition. A comparative analysis of entropy and structural parameters of related fluorides K 3 ZrF 7 - (NH 4) 2 KZrF 7 - (NH 4) 3 ZrF 7 was performed. The anomalous behavior of thermodynamic properties in the range 140−230 K is not typical for phase transitions and is accompanied by a significant change in the entropy of the crystal lattice. [ABSTRACT FROM AUTHOR]

The phase transition Pnma ↔ P 2 1 / c in K 2 TaF 7 is a strong first-order transformation of the "proper" ferroelastic origin. A huge angle of rotation of the optical indicatrix ϕ ≈ 40° and strong pre-transition phenomena in the birefringence were observed. Shear deformation and transition parameter contribute to the photoelastic effect. Heat treatments lead to the correlated changes in temperature and enthalpy. Large transition entropy Δ S = R ·ln14 is not consistent with an ordered structure model in phase Pnma. • No phase transitions were found in K 2 TaF 7 below room temperature. • The transformation Pnma ↔ P 2 1 / c is a "proper" ferroelastic of the strong first order. • A huge angle of rotation of the optical indicatrix ϕ ≈ 40° is observed. • Thermal cycling leads to correlated change in temperature and enthalpy of transition. • Large transition entropy Δ S = R· ln14 does not agree with the model of ordered structure. Optical and calorimetric experiments on K 2 TaF 7 are performed in a wide temperature range. No features were found in the behavior of the birefringence Δ n b (T), the angle of rotation of the indicatrix ϕ(T) and the heat capacity Δ C p (T) except for those associated with the Pnma ↔ P 2 1 / c phase transition. Structural transformation was characterized as strong first order "proper" ferroelastic accompanied by a huge angle ϕ ≈40° and strong pre-transition phenomena in Δ n b (T). Two contributions to the anomalies of the optical properties were found associated with the photoelastic effect and the transition parameter related linearly to the spontaneous deformation. Thermal treatments cause correlated changes in temperature and enthalpy of the phase transition, which leads to the invariance of the large magnitude of the corresponding entropy ΔS = 22 J/mol·K which does not match the model with the absence of structural disorder in the Pnma phase. [ABSTRACT FROM AUTHOR]

The orthosilicate phosphors demonstrate great potential in the field of solid-state lighting, and the understanding of the structure-property relationships depending on their versatile polymorphs and chemical compositions is highly desirable. Here we report the structural phase transformation of Ca2-xSrxSiO4:Ce3+ phosphor by Sr2+ substituting for Ca2+ within 0 ≤ x < 2. The crystal structures of Ca2-xSrxSiO4:Ce3+ are divided into two groups, namely, β phase (0 ≤ x < 0.15) and a' phase (0.18 ≤ x < 2), and the phase transition (β → α') mechanism originated from the controlled chemical compositions is revealed. Our findings verified that the phase transition Pnma (α'-phase) ↔ P21/n (β-phase) can be ascribed to the second-order type, and Sr2+ ions in Ca2-xSrxSiO4 preferentially occupy the seven-coordinated Ca2+ sites rather than the eight-coordinated sites with increasing Sr2+ content, which was reflected from the Rietveld refinements and further clarified through the difference of the Ca-O bond length in the two polymorphs of Ca2SiO4. The emission peaks of Ce3+ shift from 417 to 433 nm in the composition range of 0 ≤ x ≤ 0.8, and the difference in the decay curves can also verify the phase transformation process. Thermal quenching properties of selected Ca2-xSrxSiO4:Ce3+ samples were evaluated, and the results show that the integral emission intensities at 200 °C maintain >90% of that at room temperature suggesting superior properties for the application as white light-emitting diodes (w-LEDs) phosphors. [ABSTRACT FROM AUTHOR]

The role of anisotropy of the thermal expansion in formation of piezocaloric effect (PCE) near ferroelectric phase transitions in NH 4 HSO 4 was studied. Strong difference in linear baric coefficients and as a result in intensive and extensive PCE associated with the different crystallographic axes was found. PCE giving the main contribution to the barocaloric effect were determined at both phase transitions. Rather strong effect of the lattice dilatation on the tuning of PCE was observed. Comparative analysis of PCE at the phase transitions in different materials showed that NH 4 HSO 4 can be considered as a promising solid-state refrigerant. A hypothetical cooling cycle based on alternate using uniaxial pressure along two axes was considered. Image 1 • Strong effect of anisotropy on the piezocaloric properties of NH 4 HSO 4. • A significant difference in signs and values of linear baric coefficients. • Large piezocaloric effects at Pc↔P1 transition at low pressure. • Effective cooling cycle by using uniaxial pressure along different axes. [ABSTRACT FROM AUTHOR]

A study of heat capacity, thermal dilatation and sensitivity to hydrostatic and uniaxial pressure was carried out on single-crystal and ceramic samples of NH 4 HSeO 4. The main parameters of low-temperature successive phase transitions B 2 (T 1) ↔ incommensurate IC (T 2) ↔ ferroelectric P 1 (T 3) ↔ non-ferroelectric did not depend on the type of samples. The behavior of the volumetric strain and the results of direct measurements of T 3 (p) contributed to the resolution of the longstanding problem associated with the ambiguity of the sign of the corresponding volumetric baric coefficient. The role of thermal expansion anisotropy in the formation of the piezocaloric effect (PCE) near the ferroelectric phase transition at T 3 has been studied. Due to the strong difference in the linear baric coefficients, the main contribution to the barocaloric effect (BCE) comes from the inverse intensive and extensive PCE associated with the a- axis. Compared to a single crystal, ceramics demonstrate lower BCE values, which, however, exist in a wider temperature range, which leads to close values of integral caloric parameters. The strong decrease in both BCE and PCE at low-temperature transformations in NH 4 HSeO 4 compared to the ferroelectrics NH 4 HSO 4 and NH 4 NH 4 SO 4 is associated with a small change in entropy during three low-temperature phase transitions, ΣΔ S i = 2.52 J/mol∙K, which is a consequence of a high degree of structural ordering in selenate as a result of a high-temperature transformation at T 0 between the superionic and B 2 phases, accompanied by a giant change in entropy, Δ S 0 ≈ R ln21. [Display omitted] • Size/surface as well as anisotropy effect on thermal properties of NH 4 HSeO 4. • Gigantic entropy change associated with transformation to superionic phase. • Expansion of the temperature range of the ferroelectric phase under pressure. • Large piezocaloric effect at P 1↔paraelectric transition under very low pressure. • NH 4 HSeO 4 is a decent refrigerant for cooling devices with low heat dissipation. [ABSTRACT FROM AUTHOR]

• First study of thermal properties of nanocomposites (NH 4) 2 SO 4 + porous glasses. • Varying degree of change in sizes of pores (320→7 nm) and nanocrystallites (150→35 nm) Strong texture effect on thermal expansion of nanocomposites was observed. • Anomalous entropy decreases (12.4→8.1) J/mol∙K with decreasing pore size (320→7) nm. • Change in phase transition order in composites compared to single crystal was found. The thermal properties of nanocomposites obtained by incorporating a ferroelectric (NH 4) 2 SO 4 (AS) into porous glasses (PG) was studied for the first time. X-ray diffraction studies showed a strong increase in the ratio of the size of nanocrystallites grown in glass matrices to pore size, d cryst / d pore = 0.47→1.50→5.00, with a decrease in d pore = 320→46→7 nm. Calorimetric and dilatometric measurements showed a change from a first-order phase transition in AS single crystal to a second-order transformation in AS nanocrystallites. A restricted geometry also led to a significant decrease in the anomalous entropy in AS+PG samples compared to AS (J/mol∙K): 17.7 (AS)→12.4 (AS+PG320)→10.4 (AS+PG46)→8.1 (AS+PG7). A discussion of the nontrivial behavior of the phase transition temperature in embedded AS was carried out using the degree of PG filling, the ratio d cryst / d pore , texture, and the volumetric and linear baric coefficients for the bulk AS. [ABSTRACT FROM AUTHOR]

Single crystals of (ND 4 ) 2 MoO 2 F 4 containing 95% deuterium were produced by repeated recrystallization of (NH 4 ) 2 MoO 2 F 4 in heavy water. The effect of deuteration on the parameters of successive phase transitions was investigated by differential scanning microcalorimetry and polarization optics. X-ray analysis of the original and distorted phases was performed. It was found that deuteration does not change the sequence of crystal phases typical for (NH 4 ) 2 MoO 2 F 4 , but leads to a shift in the phase transition Cmcm → Pnma towards the tricritical point. The mechanism of phase transitions in (ND 4 ) 2 MoO 2 F 4 was associated with both the ordering and the displacement of atoms. [ABSTRACT FROM AUTHOR]

Structural phase transition P-3m1 ↔ P-1 of the first order and nonferroelectric nature was found in (NH 4 ) 2 SnF 6 at about 110 K in the process of thermal, optical, dielectric and X-ray studies. Order-disorder transformation is accompanied by large changes of entropy (Δ S 0 = 16.4 J/mol K) and volume (Δ V 0 / V ≈ 1%). The structural model associated with three orientations of NH 4 tetrahedra in P-3m1 phase and their complete ordering in P-1 phase was suggested with the entropy change (Δ S 0 = 18.3 J/mol K) close to the experimental value. A good agreement between baric coefficients measured in a direct way (d T 0 /d p = −157 K/GPa) and evaluated using entropy and volume changes at phase transition (−170 K/GPa) was found. Barocaloric effects in (NH 4 ) 2 SnF 6 are comparable with those of known solid state refrigerants and are characterised by a low-pressure need for realising their maximum values. [ABSTRACT FROM AUTHOR]

Eu2+ and Ce3+/Li+ singly doped and Eu2+/Ce3+/Li+-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the α'L-Ca2SiO4 phase with the Sr addition into Ca2Si04, and the preferred crystallographic positions of the Eu2+ and Ce3+/Li+ ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2-x)SrxSi04 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce3+/Li+ singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in die range of 250-450 nm and a blue emission peak centered at about 465 nm. When Eu2+ ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce3+,Li+,Eu2+ phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce3+ to Eu2+. The involved energy-transfer process between Ce3+ and Eu2+ and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce3+Li+,Eu2+ phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]