1,721,035 research outputs found
Ferroelastic Transition and Local Structural Properties in Cs2NaBiCl6:Mn2+ Double Perovskites
No full textHalide double perovskites (DPs) have been extensively investigated for their optoelectronic properties, which make them suitable for optoelectronic applications such as solar cells and LEDs. The unique crystal structure of DPs can accommodate a wide range of transition metals, thereby enhancing their chemical diversity and properties. However, this also calls for in-depth studies to determine how the composition affects these materials. In this study, we comprehensively inspect the structural transitions of Cs2NaBiCl6:Mn2+ by synchrotron X-ray elastic scattering analysis at room temperature (290 K) and low temperature (10 K). Both X-ray powder diffraction and pair distribution function analysis indicate that the low-temperature polymorph crystallizes in the I4/m space group. The improper ferroelastic structural transition Fm3m -> I4/m is triggered by the condensation of the primary Gamma 4 + (T1g) soft mode, and spontaneous strain analysis reveals its second-order nature. The underlying dynamics are mainly determined by the cooperative tilting of the octahedral framework, whereas cationic positions appear fixed
From Bulk to Nano: The Effect on the Persistent Luminescence
No full textPersistent luminescence materials are compounds able to glow in the dark after proper excitation. After the discovery in the 1990s of the long persistent luminescence in SrAl2O4:Eu2+,Dy3+ lasting 12 hours, the interest in this class of materials has grown quickly. Today, thousands of compounds are known to possess persistent luminescence, and some of them have found real industrial applicability. However, the mechanism driving the persistent luminescence remains somewhat unknown. The scenario is further complicated by moving from bulk materials to nanocrystals. Herein, we give an overview of the most important goals achieved in persistent luminescence materials and a critical perspective on this peculiar phenomenon at the nanoscale
Synthesis and Characterization of the CeO2/Gd2O3 mixed system by XRD, SEM and magnetic measurements
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Phase stability study of the pseudobinary system Gd2O2CO3–Nd2O2CO3 (420 °C ≤ T ≤ 850 °C, P = 1 atm. CO2)
No full textHexagonal as well as tetragonal rare earth oxycarbonates
can act as hosts for optically active ions; hence,
the knowledge of the structural modifications occurring
when foreign hosts are inserted into the parent compound is
of fundamental importance for the design of new phosphors.
In this article, a phase stability study of the pseudobinary
system Gd2O2CO3–Nd2O2CO3 at P = 1 atm. CO2 between
420 and 850 C is presented, to study the amplitude of
the existence fields of the different structures typical of rare
earth oxycarbonates. The samples were prepared by thermal
decomposition of the corresponding oxalates in CO2 atmosphere.
According to composition and temperature, all the
three structural forms reported for oxycarbonates (hexagonal,
tetragonal, and monoclinic) have been observed. Above
a certain temperature, that depends on composition and
increases with Nd amount, all the samples decompose into
the corresponding Gd–Nd-mixed oxides and crystallize into
one of the three possible structural forms typical of rare
earth sesquioxides. Structural refinements performed on the
hexagonal oxycarbonates demonstrate that the insertion
of Nd3? in Gd2O2CO3 results in a linear increase of the
lattice parameters (Vegard’s law) and in a reorganization of
the distances between and in the CO3 2- groups and the
(Nd/Gd2O2)2? layers
Structural and morphological investigation of the pseudobinary system Gd2O2CO3-Nd2O2CO3 (420°C<T<850°C)
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