Orthorhombic Room Temperature Research Articles

Inkjet Printing All Inorganic Halide Perovskite Inks for Photovoltaic Applications.

A method for synthesizing photoactive inorganicperovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are demonstrated. The ink synthesis is based on a simple wet chemical reaction and the inkjet printing protocol is a facile step by step method. The inkjet printed thin films have been characterized by X-ray diffraction, optical absorption spectroscopy, photoluminescent spectroscopy, and electronic transport measurements. X-ray diffraction of the printed quantum dot films indicates a crystal structure consistent with an orthorhombic room temperature phase with (001) orientation. In conjunction with other characterization methods, the X-ray diffractionmeasurements show high quality films can be obtained through the inkjet printing method.

Structural transitions and conductivity of BaPrO3 and BaPr0.9Y0.1O3−δ

The temperature dependence of the crystal structures of the perovskites BaPrO3 and BaPr0.9Y0.1O3−δ has been determined between room temperature and 900 °C using time-of-flight neutron powder diffraction data. The orthorhombic room temperature structures evolve to a primitive cubic cellvia three changes of symmetry Pnma → Imma → Rc → Pmm which occur at T ≈ 240, ≈ 375, and ≈ 860 °C for BaPrO3. The stability fields of the Pnma and Pmm structures are lowered markedly by the presence of yttrium on the B-site. The first and last structural transitions are assigned as continuous events, and analysis of the octahedral tilt angle order parameter suggests the latter is tricritical in nature. The Imma → Rc transition is expected to be discontinuous first order and hysteresis effects in dilatometry data support this assignment although no discontinuity is found in the refined structural parameters. Conductivity data collected under dry, oxidising conditions reveal significantly higher conductivity levels in 10% acceptor (Y or Gd) substituted samples compared to undoped BaPrO3. For the acceptor substituted samples electron holes are the dominant charge carriers and the conductivity is weakly influenced by the changing crystal structure. In the undoped BaPrO3, a crossover, probably between extrinsic (impurity-derived) and intrinsic electronic conductivity, coincides with the high temperature rhombohedral to cubic transition.

The phase diagram [formula omitted]– [formula omitted

The phase diagram gadolinium fluoride–lutetium fluoride was determined by differential scanning calorimetry (DSC) and X-ray powder diffraction analysis. Both pure components undergo a reversible first order transformation to a high temperature phase. The mutual solubility of both components is unlimited in the orthorhombic room temperature phase. The maximum solubility of Lu in the high temperature phase of GdF 3 (tysonite type) is about 20% and the maximum solubility of Gd in LuF 3 ( α - YF 3 type) is about 40%. Intermediate compositions of the low temperature phase decompose upon heating in a peritectoid reaction to a mixture of both high temperature phases.

The phase diagram YF 3–GdF 3

The binary phase diagram YF 3–GdF 3 was studied by differential scanning calorimetry (DSC). Yttrium fluoride and gadolinium fluoride show complete miscibility in all three phases (orthorhombic room temperature phase, trigonal or hexagonal high temperature phase, liquid). The transformations between room temperature and high temperature phases are of first order and occur at 1338.6 K (YF 3) or 1174.8 K (GdF 3). Melting points are 1403.1 K (YF 3) or 1525.7 K (GdF 3), respectively. The c p ( T ) curve of GdF 3 shows a λ shaped local maximum at 1333 K that might be related to a further solid phase transformation of second order.

Vibrational spectroscopic study of the structural phase transitions in Perovskite layer compounds (CH 3NH 3) 2 CdCl 4

The infrared (IR) and Raman spectra of (CH 3NH 3); CdCL 4 [C 1CdCl] are reported in the internal mode region in the 90–300 K temperature range. From an analysis of a few thermosensitive bands in the 800–2000 cm −1 range, it is concluded that C 1CdCl undergoes a transition from a tetragonal low temperature (TLT) phase to a monoclinic low temperature (MLT) phase at 160 ± 2 K. No spectroscopic manitestations are observed for a transition from an orthorhombic room temperature (ORT) phase to the TLT phase which has been reported to occur at 283 K. The observed dissimilar linewidth changes in the ν 11 (NH 3 rocking) and ν 12 (CH 3 rocking) modes around 160 K have been attributed to a dynamical motion of the methylammonium ion. The spectral parameter variations for ν 11 and ν 12 have been explained using a soft-hard mode coupling model and the value of β (order parameter critical exponent) was found to be 0.26 ± 0.05. A change in the hydrogen bonding scheme is clearly shown by the temperature dependence of the IR active mode (ν 6+ ν 9) and by the Raman frequency shifts in the ν 1 and ν 2 modes. From an Arrhenius type plot of the Raman peak intensity ratio variation for two ν 2 components, the activation energy of 845 cal mol −1 has been calculated.

Structural domains and phase transitions in organic-intercalated layer perovskite halide salts (RNH 3) 2MX 4: Optical micrography and diffraction

The structural phase transitions and the ferroelastic domain structure in the Orthorhombic Room Temperature (ORT) phase of the layer perovskite bis-(alkylammonium)-tetrachlorometallates was studied by hotstage polarizing photomicrography. The effects of the rate of cooling through the Tetragonal High Temperature (THT) → ORT structural phase transition and of a long annealing period in the THT phase upon the ORT phase domain structure were examined. The behaviour of the crystals as transmission optical diffraction gratings was also investigated. The domain structure of newly grown crystals is determined by their mechanical history. The density of domain walls is independent of the cooling rate through the phase transition and is only changed by long periods of annealing in the THT phase.

X-Ray diffraction studies of thallium selenate in the range of temperature between 305 and 12 K

Abstract The phase transition of thallium selenate (T12 SeO4) at 72 K has been investigated by X-ray diffraction measurements on polycrystalline material and single crystals. At the phase transition a large discontinuous change of all lattice constants has been observed. The orthorhombic room temperature phase has the space group symmetry Pnma. The low temperature phase has also found to be orthorhombic, however the n and the a glide planes are no longer existent, but still the systematic absences caused by the screw diad axes can be observed. Therefore the low temperature phase has the space group symmetry P212121.

Lattice dynamics and structural phase transitions in perovskite-type layer compounds. III. Quasi-elastic neutron scattering study of the cation reorientations in (CD3NH3)2MnCl4

The three disordered phases THT (tetragonal high temperature), ORT (orthorhombic room temperature) and TLT (tetragonal low temperature) of (CD3NH3)2MnCl4 have been studied by quasi-elastic neutron scattering in order to follow the reorientational dynamics of the cation CD3NH3+. Structural information has been obtained on the geometry of the motions from the incoherent structure factor measured up to Q=2.5 AA-1 for two orientations of the crystal. In particular, it has been confirmed that the cation keeps an orthorhombic configuration in the TLT phase. Furthermore, the more probable reorientational process in all three phases occurs by 90 degrees jumps about the c axis. The corresponding rate constant decreases from about 7.1*1011 jumps s-1 at 399K (THT) to 3*1011 jumps s-1 at room temperature (ORT) and to 1.8*1011 jumps s-1 at 245K (TLT). The other kinds of reorientational motions are slower by a factor of the order of ten. From these data a direct evaluation of the probabilities of the fourth orthorhombic configurations of the cation is possible.

Lattice dynamics and structural phase transitions in perovskite-type layer compounds. IV. Diffuse X-ray scattering in (CH3NH3)2CdCl4

For pt.III see ibid., vol.17, p.217 (1984). Phase transitions of (CH3NH3)2CdCl4 (MACC) have been investigated by means of diffuse X-ray scattering experiments. The diffuse scattering patterns observed in the disordered orthorhombic room temperature (ORT) and tetragonal low-temperature (TLT) phases have been interpreted through the hypothesis that disorder involves not only the methylammonium groups but also the CdCl6 octahedra perovskite-type layers. A simple model of planar disorder qualitatively accounts for the observed diffuse patterns. The data indicate that each layer can be considered as a mosaic of ordered 'clusters' involving about a hundred octahedra, and that disorder occurs between layers along the direction c perpendicular to the layer planes. On going into the monoclinic low-temperature (MLT) phase, the diffuse scattering disappears as expected for an ordered phase.

Lattice dynamics and structural phase transitions in perovskite-type layer compounds. II. The analysis of the temperature-dependent Raman spectra of (CH3NH3)2ClCl4

For pt.I see ibid., vol.16, p.1353 (1983). The low-frequency (0-500 cm-1) Raman spectra of (CH3NH3)2CdCl4 single crystal and of its deuterated homologues (CD3NH3)2CdCl4 and (CH3ND3)2CdCl4 have been recorded at various temperatures covering the domains of existence of the disordered orthorhombic room-temperature (ORT) and tetragonal low-temperature (TLT) phases. An assignment of the observed Raman-active lattice vibrations is proposed; it is based upon the observed polarisation selections, the comparison of the spectra of the various isotopic derivatives and of the spectra previously analysed for the monoclinic low-temperature phase. It is concluded that in the ORT and TLT phase disorder involves not only the orientation of the methyl ammonium groups but also the CdCl6 octahedra sublattice. The peculiar selection rules observed for a low-lying overdamped mode, assigned to oscillations of the rigid CdCl6 octahedra, are interpreted using the hypothesis of existence of short-range correlations. A new qualitative approach for the transition mechanism in this system is tentatively given.

The heat capacity of the layer compound tetrachlorobis (methylammonium) manganese—II (CH 3NH 3) 2MnCl 4, from 10 to 300k

The heat capacity of the layer compound, tetrachlorobis (methylammonium) manganese II, (CH 3NH 3) 2MnCl 4, has been measured over the range 10K < T<300K. In this region, two structural phase transitions have been observed previously by other techniques: one transition is from a monoclinic low temperature (MLT) phase to a tetragonal low temperature (TLT) phase, and the other is from TLT to an orthorhombic room temperature (ORT) phase. The present experiments have shown that the lower transition (MLT→TLT) occurs at T = 94.37±0.05K with Δ H t = 727±5 J mol −1 and Δ S t = 7.76±0.05 J K −1 mol −1, and the upper transition (TLT→ORT) takes place at T = 257.02±0.07K with Δ H t = 116±1J mol −1 and Δ S t = 0.451±0.004 J K −1mol −1. These results are discussed in the light of recent measurements on (CH 3NH 3) 2CdCl 4, and also with regard to a recent theoretical model of the structural phase transitions in compounds of this type. In addition to the structural phase transitions, (CH 3NH 3) 2MnCl 4 also undergoes magnetic ordering at T < 150K. The magnetic component to the heat capacity, as deduced from a corresponding states comparison of the heat capacity of the present compound with that of the Cd compound, is shown to be consistent with the behaviour expected for a quasi 2-dimensional Heisenberg antiferromagnet.

Ferroelectric and ferroelastic domains in barium sodium niobate an electron microscopic investigation

Abstract The domain structure of the orthorhombic room temperature phase of barium sodium niobate is examined by the electron microscopy method. It consists of ferroelectric 180°-domains and ferroelastic domains. The latter ones have the boundaries along ⟨100⟩ and ⟨010⟩ directions as referred to the axes of the tetragonal cell. Antiphase boundaries forming quadruple joins are also observed.