Band 230, Heft 11 - Special Issue: Crystal Physics / Guest Editor: Jürgen Schreuer: Dedicated to Siegfried Haussühl (1927–2014) in honor of his outstanding and pioneering contributions to crystal physics

The pyroelectric effect of four isomorphic monoclinic (space group Cc ), non-ferroelectric rare earth nitrates A 2 Ln (NO 3 ) 5 ·4H 2 O ( A = NH 4 , Rb; Ln = La, Ce) was investigated in the temperature range between 100 K and 300 K, using a home-made continuous-flow cryostat for measurements of pyroelectric currents. The symmetry-allowed temperature-dependent change of orientation of the pyroelectric vector p within the mirror plane is unusually large, showing a rotation of p of 148°, 129°, 36° and 40° for (NH 4 ) 2 La(NO 3 ) 5 ·4H 2 O, (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O, Rb 2 La(NO 3 ) 5 ·4H 2 O and Rb 2 Ce(NO 3 ) 5 ·4H 2 O, respectively, while changing the temperature from 100 K to 300 K in each case. The pyroelectric coefficients are up to ten times larger than p 3 of tourmaline. In addition, new data of the pyroelectric coefficients of Li 2 SO 4 ·H 2 O and BiB 3 O 6 and their temperature dependence are given.

Large single crystals of the tetragonal (space group I 4̅2 d ) guanidinium zinc sulfate, [C(NH 2 ) 3 ] 2 Zn(SO 4 ) 2 , were grown and the crystal structure was redetermined. Vibrational spectra obtained by Raman and IR investigations are presented, together with an assignment of the observed vibration modes. Precise refractive index data in the wavelength range from 0.365 to 1.083 μm are given. [C(NH 2 ) 3 ] 2 Zn(SO 4 ) 2 is introduced as a new stimulated Raman scattering (SRS)-active crystal with three SRS-active vibration modes with ω SRS1 ≈ 985 cm –1 , ω SRS2 ≈ 3390 cm –1 and ω SRS3 ≈ 1015 cm –1 . They allow for the generation of broadband nonlinear emission via χ (3) - (SRS and Raman-induced four wave mixing, RFWM) as well as cascaded χ (2) ↔ χ (3) - processes.

Tensorial properties such as thermal expansion, optical rotation, the electro-optic effect, elastic constants, and many more are prepared with a Windows executable, WinTensor, for rendering a graphical representation that can be viewed on a monitor or printed out for a tangible 3D model. Examples of 3D printed representation surfaces in KH 2 PO 4 and low-quartz are provided together with a summary of the state of the arts of 3D printing.

Single crystals with dimensions up to 20 × 20 × 20 mm 3 of 11 new bis(alkylammonium) zirconium bis(nitrilotriacetates) have been grown from aqueous solutions. Their elastic and thermoelastic properties were derived from ultrasonic resonant frequencies of plane-parallel plates and their shift upon variation of temperature, respectively. All of these crystal species belong to the monoclinic or orthorhombic crystal systems. The majority possesses an acentric crystal structure giving rise to piezoelectric effects, which surmount the maximum longitudinal piezoelectric effect d 111 of α-quartz by a factor of two. The pyroelectric effect of two of these specimens is about three to four times larger than π3σ$\pi _3^\sigma $ of tourmaline. In addition, the tensors of thermal expansion were determined. Owing to the dominating large size of the anion most physical properties of the salts with different cations behave quite similar. Branched or more globular alkylammonium cations generate a slightly larger mean elastic stiffness than unbranched cations.

The coefficients of thermal expansion and the complete set of elastic stiffness coefficients of monoclinic Bi 4 B 2 O 9 were determined as functions of temperature employing dilatometry and, respectively, a combination of resonant ultrasound spectroscopy and the plate resonance technique. Thermal expansion as well as elasticity of Bi 4 B 2 O 9 exhibit a pronounced anisotropy, with the directions of the maximum longitudinal elastic stiffness and of the minimal longitudinal thermal expansion running almost parallel to [1̅02]. Further, between 100 K and 535 K the principal axes system of the linear thermal expansion rotates by more than 30° around the 2-fold symmetry axis. The deviations from Cauchy-relations show a similar behavior. Both, the anisotropy and the temperature induced changes of the investigated properties are mainly controlled by the stereochemically active Bi 6 s 2 lone electron pairs. At room temperature their Wang–Liebau vectors possess preferred components within a plane that runs almost perpendicular to [1̅02]. A systematic analysis of the elastic behavior of bismuth oxides using the quasi-additivity rule for elastic S -factor reveals a general trend: With decreasing relative amount of Bi 2 O 3 the Bi 3+ cations tend to align their stereochemically active lone electron pairs in planes or eventually in one direction. With respect to the elastic behavior of the compound the alignment of the easliy deformable lone electron pairs is unfavorable and causes an elastic softening.

Copper formate tetrahydrate, Cu(HCOO) 2 ·4H 2 O, undergoes upon cooling below –38 °C a phase transition from a paraelectric (PE) into an antiferroelectric (AFE) phase, whereby its monoclinic point group 2/m is preserved and its lattice parameter c doubled. The boundary between the phases PE and AFE and the antiphase boundaries between the AFE domains have been imaged by X-ray diffraction topography (Lang technique), using a rotating-anode generator with Ag-Kα radiation. A simple cooling chamber allowed the adjustment of the transition isotherm (i.e. the phase boundary) across the plate-shaped crystal and its stepwise movement across the probe. This has been done for slices of orientation (010) and (001) with several directions of the temperature gradient. The phase boundary appears on the topographs by strong kinematical contrast, indicating considerable lattice strain in the transition region. For (001) plates the X-ray diffraction positions of the PE and AFE phase regions on both sides of the phase boundary are different so that the two regions had to be imaged in separate exposures with a small angular readjustment between them. As expected, the domain boundaries, imaged by section topography, show fringe contrast typical for antiphase boundaries. The various findings are described and discussed in detail.