Phase Transitions In Nd Research Articles

Nonlinear effects and photonic phase transitions in Nd3+-doped nanocrystal-based random lasers

The interplay between gain and scattering of light propagating in disordered media allows operation of random lasers (RLs)-lasers without conventional optical cavities. In the present paper, we review our recent contributions in this area, which include the demonstration of self-second-harmonic and self-sum-frequency generation, the characterization of Lévy's statistics of the output intensity fluctuations, and replica symmetry breaking (analogue to the spin-glass phase transition) by RLs based on nanocrystals containing trivalent neodymium ions.

Noncontact temperature‐dependent fluorescence depicting phase transition in Nd3+‐doped (K0.5Na0.5)NbO3 ceramics

AbstractA noncontact temperature measurement technique based on fluorescence variation was used to depict the temperature‐dependent evolution of phase transition of a ferroelectric material, that is, Nd3+‐doped (K0.5Na0.5)NbO3 ceramics. The slope of the fluorescence intensity curve changes dramatically in the two temperature regions of 450‐475 K and 650‐675 K, which correspond to orthorhombic‐tetragonal and tetragonal‐cubic transitions as confirmed by the temperature dependence of dielectric constant. Furthermore, the small deviations in δTO‐T and δTc indicate the good accuracy of this noncontact method. This work can guide other ergodic ferroelectrics to describe phase experience by the noncontact fluorescence method.

Ground state phase transition in the Nilsson mean-field plus standard pairing model

The ground state phase transition in Nd, Sm, and Gd isotopes is investigated by using the Nilsson mean-field plus standard pairing model based on the exact solutions obtained from the extended Heine-Stieltjes correspondence. The results of the model calculations successfully reproduce the critical phenomena observed experimentally in the odd-even mass differences, odd-even differences of two-neutron separation energy, and the $\ensuremath{\alpha}$-decay and double ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay energies of these isotopes. Since the odd-even effects are the most important signatures of pairing interactions in nuclei, the model calculations yield microscopic insight into the nature of the ground state phase transition manifested by the standard pairing interaction.

Evidence of phase transition in Nd3+doped phosphate glass determined by thermal lens spectrometry

Thermal lens spectroscopy (TLS), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) techniques were applied to the thermo-optical property analysis of a new phosphate glass matrix PANK with nominal composition 40P2O5·20Al2O3·35Na2O·5K2O (mol%), doped with different Nd(3+) compositions. This glass system, synthesized by the fusion protocol, presents high transparency from UV to the near infrared, excellent thermo-optical properties at room temperature and high fluorescence quantum efficiency. Thermal lens phase shift parameters, thermal diffusivity and the DSC signal present pronounced changes at about 61 °C for the PANK glass system. This anomalous behavior was associated with a phase transition in the nanostructured glass materials. The FTIR signal confirms the presence of isolated PO4 tetrahedron groups connected to different cations in PANK glass. As a main result, our experimental data suggest that these tetrahedron groups present a structural phase transition, paraelectric-ferroelectric phase transition, similar to that in potassium dihydrogen phosphate, KH2PO4, nanocrystals and which TLS technique can be used as a sensitive method to investigate changes in the structural level of nanostructured materials.

Atomistic mechanism of cyclic phase transitions in Nd–Fe–B based intermetallics

Mechanical milling induced atomic disorder and the mechanism of the cyclic crystal → amorphous → crystal phase transitions in a Nd 2Fe 14B intermetallic – based Nd 10Fe 85B 5 alloy were investigated. Least square first shell fitting of Extended X-ray Absorption Fine-Structure (EXAFS) data of mechanically milled samples revealed that phase evolution during mechanical milling of Nd 10Fe 85B 5 alloy occurred in two stages as a result of two dynamical effects: milling induced forced atomic mixing and enhanced diffusion due to continuous production of point defects. In the first stage of milling, atomic mixing of Nd and Fe atoms dominated, resulting in extensive chemical and structural disorder in the initially ordered intermetallic, followed by amorphization. The second stage of milling was characterized by a remarkable increase in point defect density. Enhanced diffusion resulted in redistribution of alloy atoms and annihilation of these point defects leading to the precipitation of α-Fe nanocrystals in the amorphous matrix. Thus the time evolution of defect structures formed during mechanical milling and their atomic scale interactions led to the cyclic phase transitions in the Nd 10Fe 85B 5 alloy. These milling induced changes in atomic order were found to strongly influence magnetic properties. Crystallization of mechanically milled alloy and effect of annealing parameters on magnetic properties was also analyzed.

ChemInform Abstract: Crystal Structure of Ln1/3NbO3 (Ln: Nd, Pr) and Phase Transition in Nd1/3NbO3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Crystal structure of Ln1/3NbO 3 ( Ln=Nd, Pr) and phase transition in Nd 1/3NbO 3

The crystal structure of the A-site deficient perovskite Ln 1/3NbO 3 ( Ln=Nd, Pr) at room temperature has been determined, for the first time, as orthorhombic in space group Cmmm using high-resolution neutron powder diffraction. Pertinent features are the alternation of unoccupied layers of A-sites and layers partly occupied by Ln cations, as well as out-of-phase tilting of the NbO 6 octahedra around an axis perpendicular to the direction of the cation/vacancy ordering. The phase transition behaviour of Nd 1/3NbO 3 has also been studied in situ. This compound undergoes a continuous phase transition at around 650 °C to a tetragonal structure in space group P4/ mmm due to the disappearance of the octahedral tilting. The analysis of spontaneous strains shows that this phase transition is tricritical in nature.

Magnetic phase transitions in Nd 1− xY xMn 2Ge 2 (0 ≤ x ≤ 0.6)

The structure and magnetic properties of Nd 1− x Y x Mn 2Ge 2 (0.0≤ x≤0.6) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2Si 2-type structure with space group I4/ mmm. Substitution of Y for Mn led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Y for Nd in NdMn 2Ge 2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering.

Effects of oxygen deficit, Sr, Ti and Cr substitution on the antiferro–ferromagnet transition in Nd 0.6Ca 0.4MnO 3

We have investigated phase transitions in Nd 0.6Ca 0.4− x Sr x (Mn 1− y M y )O 3− γ (M=Cr, Ti) by measurement of magnetization and electrical transport in magnetic fields up to 12 T. It is shown that oxygen deficit up to γ=0.03, Sr doping up to x=0.05 and Cr doping up to y=0.03 lead to strong decrease of magnetic field which induces antiferro–ferromagnet (A–F) transition. Samples with chromium content above y=0.03 and Sr-content above x=0.1 are ferromagnets whereas in the samples with large oxygen deficit an antiferromagnetic structure is stabilized. The magnetization measurements indicate the ferromagnetic coupling between manganese and chromium ions.

Polarized neutron scattering investigation of successive magnetic phase transitions in Nd 2CuO 4 and Nd 1.87Ce 0.19CuO 4

Successive magnetic phase transitions in Nd 2CuO 4 and Nd 1.87Ce 0.19CuO 4 are investigated by polarized neutron scattering. It is shown that Ce doping decrease the temperature of three-dimensional ordering of Cu ions. The spin reorientation phase transitions in Nd 1.87Ce 0.13CuO 4 are suppresed by the Ce doping. Polarized neutron scattering gives a detailed information about the orientation of magnetic moments, but cannot distinguish between collinear and noncollinear structures.

On the crystal distortion in tetragonal Nd2CuO4

X-ray diffraction measurements have been performed on single crystal Nd 2 CuO 4 in order to re-examine the structural distortion from the tetragonal symmetry which could trigger the successive magnetic phase transitions in Nd 2 CuO 4 . Previously reported reflections such as ( 1 2 , 1 2 , 3) which are forbidden in the I4/mmm space group were not detected. However, we did observe a peak at the ( 1 2 , 1 2 , 3) position when the incident beam was contaminated by excessive higher order components. Since there is no distortion from the I4/mmm symmetry there must be another mechanism for the successive magnetic phase transitions in Nd 2 CuO 4 .

Optical, X‐ray, and calorimetric studies of phase transitions in ND4BeF3

AbstractPhase transitions in ND4BeF3 crystals at T1 = 330 and T2 = 245 K were studied by specific heat (DSC) and X‐ray lattice parameters measurements in function of temperature. These ferroelastic transitions are accompanied by anomalous heat absorption, sudden changes in the unit cell parameters and crystal symmetry. Formation of domain structure in particular phases examined under a polarizing microscope is also described. Domain walls of the type (100), (010), and (001) observable at room temperature indicate on the triclinic symmetry of the Phase II. Above T1 the crystal becomes orthorhombic. First‐order phase transition at T2 causes the symmetry of the crystal in the Phase III to be monoclinic with the c‐axis unique. The phase transition diagram is proposed and compared with the phase situation in nondeuterated NH4BeF3 crystals.