We present a comprehensive review of the material properties of cadmium zinc telluride (CZT, Cd1ˇxZnxTe) with zinc content xa 0:1‐0.2. Particular emphasis is placed on those aspects of this material related to room temperature nuclear detectors. A review of the structural properties, charge transport, and contacting issues and how these are related to detector and spectrometer performance is presented. A comprehensive literature survey and bibliography are also included. # 2001 Elsevier Science B.V. All rights reserved.

Cadmium zinc telluride and its use as a nuclear radiation detector material

Feature size is a natural determinant of material properties. Its design offers the technological perspectives for material improvement. Grain size, crystallite size, domain width, and structural defects of different nature constitute the classical design elements. Common ferroelectric ceramics contain micrometer grain sizes and submicrometer domain widths. Domain wall mobility is a major contribution to their macroscopic material properties providing approximately half of the macroscopic output in optimized materials. The extension into the dynamic nanoworld is provided by relaxor ferroelectrics. Ionic and nanoscale field disorders form the base to a state with natural nanometer-size polar structures even in bulk materials. These polar structures are highly mobile and can dynamically change over several orders of magnitude in time and space being extremely sensitive to external stimuli. This yields among the largest dielectric and piezoelectric constants known. In this feature article, we want to outline how lead-free relaxors will offer a route to an environmentally safer option in this outstanding material class. Properties of uniaxial, planar, and volumetric relaxor compositions will be discussed. They provide a broader and more interesting scope of physical properties and features than the classical lead-containing relaxor compositions.

Lead-Free Relaxor Ferroelectrics

Tensor Analysis for Physicists. By J.A. Schouten. Second edition. Pp. xii, 277. 30s. 1954. (Geoffrey Cumberlege, Oxford University Press.)

Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Deep Ultraviolet Nonlinear Optical Materials

In the past few years magneto-optical flux imaging (MOI) has come to take an increasing role in the investigation and understanding of critical current densities in high-Tc superconductors (HTS). This has been related to the significant progress in quantitative high-resolution magneto-optical imaging of flux distributions together with the model-independent determination of the corresponding current distributions. We review in this article the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials and analyse systematically the properties determining the spatial distribution and the magnitude of the supercurrents. First of all, the current distribution is determined by the sample geometry. Due to the boundary conditions at the sample borders, the current distribution in samples of arbitrary shape splits up into domains of nearly uniform parallel current flow which are separated by current domain boundaries, where the current streamlines are sharply bent. Qualitatively, the current pattern is described by the Bean model; however, changes due to a spatially dependent electric field distribution which is induced by flux creep or flux flow have to be taken into account. For small magnetic fields, the Meissner phase coexists with pinned vortex phases and the geometry-dependent Meissner screening currents contribute to the observed current patterns. The influence of additional factors on the current domain patterns are systematically analysed: local magnetic field dependence of jc(B), current anisotropy, inhomogeneities and local transport properties of grain boundaries. We then continue to an overview of the current distribution and current-limiting factors of materials, relevant to technical applications like melt-textured samples, coated conductors and tapes. Finally, a selection of magneto-optical experiments which give direct insight into vortex pinning and depinning mechanisms are reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/65/5/202/pdf

Magneto-optical studies of current distributions in high-Tc superconductors

$\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}\mathrm{\text{\ensuremath{-}}}x{\mathrm{PbTiO}}_{3}$ ($x=4.5%\char21{}12%$) relaxor ferroelectric crystals have been studied by means of acoustic emission (AE) in the 400\char21{}540 K temperature range. An anomalous AE activity independent of the ground state relaxor/morphotropic/ferroelectric crossover has been revealed at around 500 K, and it is associated with the ``waterfall'' feature related to the existence of polar nanoregions (PNRs). The 500 K AE anomaly is attributed to local martensitelike cubic-to-tetragonal ferroelectric transitions within the PNRs imbedded in a nonpolar (cubic) matrix.

Phase transition at a nanometer scale detected by acoustic emission within the cubic phase Pb(Zn1/3Nb2/3)O3-xPbTiO3 relaxor ferroelectrics.

Crystal growth and applications of mercuric iodide

The restored strain energy in $\mathrm{Pb}{\mathrm{Zn}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}$ (PZN) and $9%\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$-doped PZN (PZN-9%PT) relaxor crystals has been studied by means of acoustic emission (AE). Two types of AE activity signals have been recorded: (i) related to temperature- or electric-field-induced macroscopic phase transitions and (ii) associated with formation/disappearance of intrinsic polar nanoregions. Monitoring of AE under varying [001] electric fields has allowed a unique in situ observation of a low-field $(1\phantom{\rule{0.3em}{0ex}}\mathrm{kV}∕\mathrm{cm})$ irreversible orthorhombic-to-${M}_{C}$ phase transition within the morphotropic phase boundary region of PZN-9%PT.

Acoustic emission study of phase transitions and polar nanoregions in relaxor-based systems: Application to the PbZn1/3Nb2/3O3 family of single crystals

A new generation of oxide crystals is emerging for electro-optic Q-switching or control of high-power pulsed lasers. Unlike the acousto-optic Q-switches in which the total turn-off time is limited by the duration of sound wave propagation (110–220 ns/mm) across the beam diameter, the electro-optic devices provide a short (<10 ns) response needed for minimum losses. Extinction ratios of better than 100 : 1 for electro-optic crystals ensure their reliable hold-off. By contrast, acousto-optic devices are characterized by single-pass dynamic losses of approximately 40%, which hinders their use in high-gain lasers. The basic principles of electro-optic Pockels cells are discussed. The performance characteristics of Q-switching for traditional electro-optic materials [deuterated potassium dihydrogen phosphate (DKDP), lithium niobate (LNB)] and other new electro-optic crystals, such as barium metaborate (BBO) and crystals belonging to the langasite (LGS) and potassium titanyl phosphate (KTP) families, are reviewed comparatively. Particular emphasis is placed on KTP-type electro-optic crystals, primarily on rubidium titanyl phosphate RbTiOPO4 (RTP), which stand out in their ability to provide Q-switching at extremely high frequencies or repetition rates up to 200 kHz. The use of both X- and Y-oriented double crystals as Q-switches in order to combine large electro-optic coefficients and low quarter-wave hold-off voltages with excellent thermal stability of the device is considered.

Oxide crystals for electro-optic Q -switching of lasers

BaTiO3 crystals were studied by means of the acoustic emission during thermal cycling through 300–700 K range. In addition to pronounced acoustic emission at the ferroelectric phase transition temperature Tc≈400 K, also nucleation of nanoclusters was detected at somewhat smeared Burns temperature Td≈530–570 K and their local freezing at T∗≈506 K. Bias electric field shifts the T∗ and Tc linearly up, T∗ more steeply than Tc. Except for its much faster cluster dynamics than that of classical relaxor materials, BaTiO3 shows many relaxor-like features in its paraelectric phase.

Michael Roth

Papers

Phase transition at a nanometer scale detected by acoustic emission within the cubic phase Pb(Zn1/3Nb2/3)O3-xPbTiO3 relaxor ferroelectrics.

Crystal growth and applications of mercuric iodide

Acoustic emission study of phase transitions and polar nanoregions in relaxor-based systems: Application to the PbZn1/3Nb2/3O3 family of single crystals

Oxide crystals for electro-optic Q -switching of lasers

Relaxor-like behavior of BaTiO3 crystals from acoustic emission study