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MgO nanocubes are well-suited for the study of defects and interfaces inside metal oxide powders and ceramics. We evaluated the synthesis of MgO nanocubes via flame spray pyrolysis (FSP) and compared the structural and spectroscopic particle properties with materials obtained by chemical vapor synthesis (CVS). Characterization of the as-synthesized and vacuum annealed powder samples revealed slightly larger particle sizes for the FSP material that is absolutely comparable to CVS powders in terms of the particles structural definition, morphology and crystallinity. Moreover, optical absorption and photoluminescence emission studies show fingerprints, which are characteristic of MgO nanocrystals with a high abundance of grain corners, kinks and edges. The opportunity to synthesize MgO nanoparticles of high structural definition via FSP at significantly larger production rates and lower costs compared to CVS carries great potential to upscale powder production to generate MgO based functional oxide nanocomposites for ceramics and catalysis.

We report the observation of tens of minor lines of the combinational spin-flip Raman scattering in a CdTe:Mn quantum well by means of the high-resolution optical spectroscopy. Classification of this manifold leads to four characteristic values of energy, that correspond to four different types of pair clusters of Mn ions: the nearest, second, third, etc., neighbors. All the four energies show up in a single experiment with a very high precision, providing experimental grounds for a deeper understanding of the $d\ensuremath{-}d$ exchange interactions in a diluted magnetic semiconductor and demonstrating the capacity of the employed method. The major (nearest-neighbor) exchange constant ${J}_{1}=6.15\ifmmode\pm\else\textpm\fi{}0.05$ K was found to consent with its previously reported value. Other detected characteristic energies are as follows ($\ifmmode\pm\else\textpm\fi{}0.05$ K): ${J}_{(2)}=1.80$ K, ${J}_{(3)}=1.39$ K, ${J}_{(4)}=0.81$ K.

A key question in the field of ceramics and catalysis is how and to what extent residual water in the reactive environment of a metal oxide particle powder affects particle coarsening and morphology. With X‐ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), we investigated annealing‐induced morphology changes on powders of MgO nanocubes in different gaseous H2O environments. The use of such a model system for particle powders enabled us to describe how adsorbed water that originates from short exposure to air determines the evolution of MgO grain size, morphology, and microstructure. While cubic nanoparticles with a predominant abundance of (100) surface planes retain their shape after annealing to T = 1173 K under continuous pumping with a base pressure of water p(H2O) = 10−5 mbar, higher water partial pressures promote mass transport on the surfaces and across interfaces of such particle systems. This leads to substantial growth and intergrowth of particles and simultaneously favors the formation of step edges and shallow protrusions on terraces. The mass transfer is promoted by thin films of water providing a two‐dimensional solvent for Mg2+ ion hydration. In addition, we obtained direct evidence for hydroxylation‐induced stabilization of (110) faces and step edges of the grain surfaces.

${\mathrm{BaBiO}}_{3}$ (BBO) is well known as the parent material for the high-${T}_{c}$ superconducting compounds ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{BiO}}_{3}$ and ${\mathrm{BaPb}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{O}}_{3}$. In its pristine state, BBO is a charge-ordered (CO) insulator, resulting from a static breathing distortion of the ${\mathrm{BiO}}_{6}$ octahedra with alternating long and short bond lengths. Recently, it has been reported that the CO state is suppressed for BBO films grown on ${\mathrm{SrTiO}}_{3}$ (STO) below a thickness of approximately 4 nm, possibly resulting in a metallic phase. While we do confirm structural modifications in our BBO/Nb:STO samples in this thickness range by Raman spectroscopy and electron diffraction, in situ photoemission evidences that these changes are accompanied by a Bi deficit and that the films remain insulating. We hence conclude that, in line with previous findings for the BBO/STO interface, the thickness-controlled suppression of the CO state is not purely driven by the two-dimensional confinement but rather originates from modifications of the composition and structure inherent to the epitaxial growth of BBO on ${\mathrm{SrTiO}}_{3}$(001).

The orthorhombic rare-earth manganate ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{Ho}}_{x}{\mathrm{MnO}}_{3}$ ($x\ensuremath{\ge}0.15$) exhibits multiferroism below ${T}_{\text{MF}}$ $\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, with a static electric polarization caused by a cycloidal spin order. We observe transient disorder effects in the crystal lattice in a very narrow temperature interval at the onset of the multiferroic ordering. This disorder manifests itself in a distinct transitory violation of the symmetry selection rules for lattice vibration modes in Raman spectroscopy: polarized Raman spectra show a clear increase of the intensity of symmetry-forbidden phonon modes. Possible scenarios of transient disorder in a narrow temperature range are discussed, with special reference to the development of 90\ifmmode^\circ\else\textdegree\fi{} domain walls in ${\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{Ho}}_{x}{\mathrm{MnO}}_{3}$, which are associated with the onset of a spontaneous reorientation of the spin cycloids with decreasing temperature.

${\text{Eu}}_{1\ensuremath{-}x}{\text{Ho}}_{x}{\text{MnO}}_{3}$ with $xl0.5$ has an orthorhombic perovskite structure, where the partial substitution of europium by holmium increases the orthorhombic distortion and changes the low-temperature magnetic structure from canted antiferromagnetic to the multiferroic ground state with cycloidal spin arrangement for $xg0.2$. We employ polarized, temperature-dependent Raman spectroscopy to study the lattice dynamics and spin-phonon coupling (SPC) effects for the two representative compositions $x=0.1$ and $x=0.3$. We observe an enhancement of phonon frequencies by ${\text{Ho}}^{3+}$ substitution and we use the ${A}_{g}(4)$ mode as a measure to evaluate the orthorhombic distortion angle $\ensuremath{\theta}$. SPC manifests itself as mode-specific softening for $Tl100$ K, induced by the magnetic ordering of ${\text{Mn}}^{3+}$ spins. Furthermore, we present evidence that the hitherto elusive Raman peak at $\ensuremath{\approx}650\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ is a phonon of ${B}_{3g}$ symmetry and ascribe it to the ${B}_{3g}(1)$ out-of-phase ${\text{MnO}}_{6}$-breathing mode. We show that this mode has the strongest SPC effect of all observed phonon modes, a fact which we explain by the participation of the apical O(1) ions, modulating the Mn-O(1)-Mn bond whose SPC contribution was hitherto not accessible. Finally, we present a quantitative evaluation of the SPC contribution by the antiferromagnetic plane-to-plane coupling through the Mn-O(1)-Mn bonds and discriminate if from the in-plane ferromagnetic Mn-O(2)-Mn part.