Specific Crystallographic Orientation Relationship Research Articles

Novel (Ti, W)C–SiC–WSi2 ceramics fabricated via in situ reaction spark plasma sintering at 1600 °C

Novel (Ti, W)C–SiC–WSi2 ceramics were fabricated by in situ reaction spark plasma sintering (SPS) at 1600 °C using (Ti, W)C and Si powders. The effect of Si content on densification behavior, microstructures, and mechanical properties was investigated. The in situ reaction and the formation of carbon vacancies reduced the sintering temperature. The densification mechanism of (Ti, W)C-based ceramics transforms from reaction to grain-boundary sliding and diffusion. The WSi2 and primary SiC generated by in situ reactions are distributed along the grain boundaries and have a specific crystallographic orientation relationship. Intragranular secondary SiC formed because of rapid densification, grain-boundary diffusion, and (Ti, W1−y)C1−x particle migration. This multiscale particle-reinforced microstructure can improve the mechanical properties of (Ti, W)C ceramics, giving the TW10S (4.80 wt% SiC–5.01 wt% WSi2) good sintering performance, a fine-grained microstructure, high hardness (23.3 ± 1.6 GPa), and flexural strength (425 ± 24 MPa). The SiC and WSi2 produced through in situ reactions have exceptional intrinsic oxidation resistance, allowing the ceramics to achieve outstanding oxidation resistance.

Influence of the hierarchical architecture of multi-core iron oxide nanoflowers on their magnetic properties

Magnetic properties of superparamagnetic iron oxide nanoparticles are controlled mainly by their particle size and by their particle size distribution. Magnetic properties of multi-core iron oxide nanoparticles, often called iron oxide nanoflowers (IONFs), are additionally affected by the interaction of magnetic moments between neighboring cores. The knowledge about the hierarchical structure of IONFs is therefore essential for understanding the magnetic properties of IONFs. In this contribution, the architecture of multi-core IONFs was investigated using correlative multiscale transmission electron microscopy (TEM), X-ray diffraction and dynamic light scattering. The multiscale TEM measurements comprised low-resolution and high-resolution imaging as well as geometric phase analysis. The IONFs contained maghemite with the average chemical composition gamma-Fe_{2.72pm 0.02}O_4. The metallic vacancies located on the octahedral lattice sites of the spinel ferrite structure were partially ordered. Individual IONFs consisted of several cores showing frequently a specific crystallographic orientation relationship between direct neighbors. This oriented attachment may facilitate the magnetic alignment within the cores. Individual cores were composed of partially coherent nanocrystals having almost the same crystallographic orientation. The sizes of individual constituents revealed by the microstructure analysis were correlated with the magnetic particle sizes that were obtained from fitting the measured magnetization curve by the Langevin function.

Synthesis of ultrafine dual-phase structure in CrFeCoNiAl0.6 high entropy alloy via solid-state phase transformation during sub-rapid solidification

High entropy alloys (HEAs) with superb mechanical properties have been traditionally produced by solidification and subsequent heat treatment. In this paper, we demonstrate a new route via one-step process using sub-rapid cooling. Under proper cooling rates, the CrFeCoNiAl0.6 HEA could form ultrafine FCC+BCC dual-phase structure. By varying cooling rate, we can control the fraction of the BCC phase and refinement of FCC microstructures that have tunable mechanical properties in yield strength and hardness ranging from ∼580 to ∼1460 MPa and ∼260 to ∼550 Hv. We show that the structure-property-processing relation originates from the sideplate microstructures formed during fast cooling that have specific crystallographic orientation relationship between the FCC and BCC phases and chemical segregation. This work provides a new setting for better understanding of the solid-state phase transformation in HEAs under sub-rapid solidification conditions as well as a novel method for development of high-performance HEAs.

The Role of Parent Phase Topology in Double Young–Kurdjumow–Sachs Variant Selection during Phase Transformation in Low-Carbon Steels

The present paper investigates the role of parent phase topology on a crystallographic variant selection rule. This rule assumes that product phase nuclei appear at certain grain boundaries in the parent structure, such that a specific crystallographic orientation relationship is observed with both parent grains at either side of the grain boundary. The specific crystallographic orientation correspondence considered here is the Young–Kurdjumow–Sachs (YKS) orientation relationship <112>90° (which exhibits 24 symmetrical equivalents). The aforementioned relationship is characteristic of phase transformations in low-carbon steel grades. It is shown that, for different parent phase textures, ~20% of the grain boundaries comply with the double YKS condition allowing for a tolerance of 5°, ignoring the presence of topology in the parent phase microstructure. The presented model allows for connecting the presence of a specific parent phase topology with the condition of the double YKS variant selection rule in a number of practical cases: (i) for hot rolled Ti–Interstitial Free (IF) steel with and without Mn addition, (ii) for cold rolled IF steel exhibiting very strong texture memory after forward and reverse α ⇌ γ phase transformation and (iii) for a martensitic transformation in a Fe–8.5% Cr steel. It is shown that the double YKS variant selection criterion may explain several specific features of the observed transformation textures, while assuming a non-correlated arbitrary pair topology of the parent austenite structure (implying that for N parent orientations N/2 pairs are selected in an arbitrary manner).

Iron oxide inclusions and exsolution textures of rainbow lattice sunstone

Abstract. Iron oxide inclusions and exsolution lamellae in rainbow lattice sunstone (RLS) from Harts Range, Australia, are examined using optical and electron microscopy and single-crystal X-ray diffraction (SC-XRD). Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analyses show a bulk composition of An1.4Ab14.8Or83.0Cn0.8 with < 200 ppmw (parts per million weight) of Fe. Two stages of exsolution can be identified in RLS from the bimodal distribution in the size and shape of the exsolution lamellae. Micron-scaled Albite-twinned oligoclase spindles (An27Ab72Or1) first exsolved at ∼ 650 ∘C were followed by nanoscaled Pericline-twinned albite films (∼ Ab100) below 500 ∘C that create adularescence. The albite films inherited and preserved the monoclinic tetrahedral framework of the orthoclase matrix (An0.3Ab11.5Or87.3Cn0.9) as further ordering was completely inhibited by coherent-interface strain after exsolution. All the exsolution lamellae are pristine and strain-controlled with no signs of any deuteric or hydrothermal alteration, indicating the iron in the magnetite inclusions was not introduced by an external fluid. The magnetite inclusions nucleated around the same time as the exsolution of oligoclase spindles likely due to the reduction of Fe3+ to Fe2+ in the feldspar lattice. Magnetite films following the specific crystallographic orientation relationship (COR) of {111}Mt∥{100}Or and 11‾0Mt∥001Or grew to extraordinarily large sizes due to the near perfect lattice match at the interface with the orthoclase host. Some thinner magnetite films were oxidized into hematite during weathering of the host rock. RLS reveals a new mechanism for the formation of the flaky hematite inclusions in feldspars, which may explain the enigmatic origin of aventurescence observed in many other sunstones and red-clouded feldspars.

Mechanistic insights into interface-facilitated dislocation nucleation and phase transformation at semicoherent bimetal interfaces

The nucleation of lattice dislocations and interface sliding at bimetal interfaces are two fundamental mechanisms of plasticity that are responsible for the mechanical responses of nanostructured materials; however, the interface-facilitated phase transformation is rarely considered owing to its relatively high energy barrier for activation. Taking the bimetal hcp/bcc interfaces with Pitch-Schrader and Burgers orientation relationships (ORs) as an illustration, we show that both non-basal dislocation nucleation and hcp-to-bcc phase transformation can be activated at the interface under external loading when the basal slip systems are effectively suppressed. The non-basal dislocation nucleation is shown to be closely related to the dynamic evolution of misfit dislocation patterns at the semicoherent interface, in which the 1/6[022¯3¯] pyramidal dislocation is not strictly parallel to the (011¯1) stacking fault plane owing to the corrugated feature. In contrast to non-basal dislocation nucleation, phase transformation requires specific crystallographic ORs of the constituent metals under certain loading conditions, which corresponds to the process of alternate shuffle and shear deformation that involves atomistic migration. To further reveal the competition between non-basal dislocation nucleation and phase transformation, a series of twisted interface models were constructed to systematically investigate the optimal condition of the interface geometry for phase transformation. The phase transformation occurred only when the dislocation nucleation was further hindered at some specific twist angles, suggesting a strong dependence of phase transformation on the interface structure. These findings provide a foundation to the atomistic mechanism of various interface-mediated deformation and a solution to tune interface-facilitated plasticity via interface engineering.

Crystallographic and shape orientations of magnetite micro-inclusions in plagioclase

Plagioclase hosted, oriented magnetite micro-inclusions are a frequently observed phenomenon in magmatic and metamorphic rocks. Understanding the orientation relationships between these inclusions and the plagioclase host is highly relevant for interpreting paleomagnetic measurements. The systematics of the shape and crystallographic orientation relationships between needle- and lath-shaped magnetite micro-inclusions and their plagioclase host from oceanic gabbro were investigated using optical microscopy including universal stage measurements, scanning electron microscopy, and crystal orientation analysis by electron backscatter diffraction. The magnetite inclusions show preferred shape orientations following six well-defined directions and with specific crystallographic orientation relationships to the plagioclase host. These relationships are rationalized based on angular and dimensional similarities between the crystal structures of magnetite and plagioclase, which favor the parallel alignment of oxygen layers with similar lattice spacing in both phases. The parallel alignment of oxygen layers in plagioclase and magnetite can be traced back to the oriented nucleation of magnetite, which occurs by the accommodation of FeO6 octahedra in six-membered rings of SiO4 and AlO4 tetrahedra of the plagioclase structure. The orientation systematics of the magnetite micro-inclusions is related to four orientation variants for placing the FeO6 octahedra into the plagioclase structure.

Heterogeneous nucleation of M2B-type borides (M = Cr, Fe) attached to TiB2 and Ti(C,N) particles in as-cast high borated steel

Here we for the first time reported the heterogeneous nucleation of orthorhombic M2B-type borides (M = Cr, Fe) attached to TiB2 and Ti(C,N) particles with a specific crystallographic orientation relationship (OR) in as-cast boron-containing steel. The ORs were identified as 0001TiB2∥1¯12¯M2B, 12¯10TiB2∥311¯M2B and 001TiCN∥136¯M2B, 100TiCN~∥31¯0M2B. The transmission electron microscopy characterization and lattice misfit calculation showed that the interfaces of TiB2/M2B and Ti(C,N)/M2B were semi-coherent. The heterogeneous nucleation efficiency was investigated in terms of an interfacial energy calculation based on the misfit dislocation theory.

Annealing twins in high purity aluminium processed by dynamic equal channel angular pressing

Annealing twins are synthesised in high purity aluminium processed by dynamic equal channel angular pressing during annealing. Annealing twins and recrystallised grains encircling the twins have specific crystallographic orientation relationships with the deformed matrix grains: approximately 35°–50°<110> for the twins and 30°–45°<100> for the recrystallised grains. Stored energy during dynamic pressing, and the crystallographic orientation between annealing twins and the deformed matrix, strongly affect twin growth during annealing.

Effects of gas flow on detailed microstructure inhomogeneities in LPCVD TiAlN nanolamella coatings

Depositing homogeneous TiAlN coatings with a high Al content on cutting tool inserts is a challenging task. In this work, high-Al cubic Ti1-xAlxN coatings (average x = 0.8) with periodic Ti(Al)N (x = 0.5) and Al(Ti)N (x = 0.9) nanolamellae structure were synthesized by low pressure chemical vapour deposition (LPCVD) with different gas flow velocities, and the detailed microstructure was investigated by electron microscopy and simulations. Using a high gas flow rate, the columnar TiAlN grains with regular periodic nanolamella structures disappeared, the coating became enriched in Ti and hexagonal AlN (h-AlN) formed in the coating. The high Ti content is suggested to be caused by the high gas flow rate that increases the mass transport of the reactants. However, this does not influence the Al-deposition much as it is mainly limited by the surface kinetics due to the relatively low deposition temperature. Density functional theory (DFT) modelling and electron microscopy showed that h-AlN tends to form on the Ti(Al)N phase with a specific crystallographic orientation relationship. The Ti enrichment due to high gas flow rate promotes the formation of h-AlN, which therefore deteriorates the nanolamella structure and causes the disappearance of the columnar TiAlN grains. Thus, by designing the CVD process conditions to avoid too high gas flow rates, homogenous TiAlN coatings with high Al content and nanolamella structures can be deposited, which should yield superior cutting performance.

Pulsed Laser Condensation of Dense Cubic ZnO with Unique Luminescence, Vibrations, and Interphase Interfaces

Dense ZnO with a high-pressure stabilized rocksalt (R)-type structure was fabricated by pulsed laser ablation of bulk wurtzite (W)-type ZnO under a rather high peak power density for a prolonged time in a vacuum. Such dynamic synthesis of R-ZnO relies on effective six-coordination of Zn with O atoms in a laser plume for homogeneous nucleation of R-besides the W-type structure with ZnO4 tetrahedra. The deposit on amorphous silica contains ca. 10% dense R-ZnO with internal compressive stress up to 22.5 GPa based on the X-ray lattice parameter. Transmission electron microscopic observations further indicated the polymorphic condensates are (011)R, (112̅0)W, and (0001)W faceted for mutual coalescence to reach specific crystallographic orientation relationships which are different from that due to R → W transformation, all with an energetically favorable three-dimensional match of lattice planes. The R-type islands up to 100 μm in size on silica substrate showed Raman bands at 800, 1380, and 1607 cm–1 and strong photoluminescence at 545 nm due to ZnO6 octahedra in the cubic crystal field.

On the forbidden and the optimum crystallographic variant of rutile in garnet

In many inclusion–host systems with similar oxygen packing schemes, the optimum crystallographic orientation relationship (COR) between the inclusion and the host is mostly determined by matching the similar oxygen sublattices of the two structures. In contrast, the prediction of the optimum COR or even just the rationalization of the observed COR(s) between an inclusion and host with incompatible oxygen sublattices, like rutile–garnet, is not straightforward. The related documentation for such cases is therefore limited. Given the abundant crystallographic data for the rutile–garnet system acquired by transmission electron microscopy and electron backscatter diffraction methods recently, this problem can now be examined in detail for the critical structural factors dictating the selection of optimum COR in such a structurally complicated system. On the basis of the unconstrained three-dimensional lattice point match and structural polyhedron match calculated for the observed CORs, it becomes clear that the prerequisite of optimum COR for rutile (rt) in garnet (grt) is to have most of their octahedra similarly oriented/inclined in space by aligning 〈103〉rt and 〈111〉grt for needle extension growth. Further rotation along the 〈103〉rt//〈111〉grt direction then leads to the energetically most favorable COR-2 variant with a good lattice point match defined by the coincidence site lattice (CSL) and a good topotaxial match of the constituent polyhedra at the CSL points, leaving unfavorable COR-1′ in the forbidden zones. This understanding sheds light not only on hierarchical energetics for the selection of inclusion variants in a complicated inclusion–host system, but also on yet-to-be-explored [UVW]-specific CORs and hetero-tilt boundaries for composite materials in general.

Dynamic precipitation in a Mg–Gd–Y–Zr alloy during hot compression

Dynamic precipitation of a Mg–8.3Gd–2.6Y–0.4Zr (wt.%) alloy during hot compression was systematically investigated in the present work. For this purpose, the compression tests were conducted at temperatures ranging from 300°C to 500°C and strain rates varying from 0.001s−1 to 1s−1. Results revealed that the dynamic precipitation of equilibrium β phase, i.e., Mg5(Gd,Y) phase, was sensitive to the deformation temperature rather than the strain rate. The precipitation took place during compression in the temperature range of 300–400°C, whereas it did not occur when temperature exceeded 450°C. The dynamically precipitated β phase showed an irregular shape and did not possess any specific crystallographic orientation relationship with the matrix. The precipitates distributing at the dynamically recrystallized (DRXed) grain boundaries could severely suppress the growth of DRXed grains due to pinning effect, which therefore formed ultra-fine DRXed grains with sizes of ~200–400nm.

Crystallization of Ni–P Fabricated by Electroless Deposition: Microscopic Mechanism

ABSTRACTWe investigate the crystallization of amorphous Ni–P with near-eutectic composition, fabricated by electroless plating as a 10 µm thick continuous layer. Aiming to understand phase transformations that occur upon heating and, in particular, the microscopic mechanism of crystallization, we combine a variety of complimentary characterization techniques. DSC (differential scanning calorimetry) during isothermal heating reveals the crystallization kinetics. Conventional-, high-resolution-, and analytical TEM (transmission electron microscopy) and TEM-based electron diffraction provide high-spatial-resolution information on phase nucleation and spatial distribution of atom species, particularly the crystallography of the nucleating crystalline phases (Ni3P and Ni) and the spatial distribution of phosphorus in the partially and completely crystallized alloy. Our results indicate that crystallization proceeds by homogeneous nucleation of Ni3P grains. Internally, these exhibit a microstructure of radially oriented subgrains containing Ni nano-platelets in a specific crystallographic OR (orientation relationship) with Ni3P. However, the preferred Ni–Ni3P OR differs from those reported in the literature for similar material. Combining our observation on the structure and microstructure of partially and completely crystallized Ni–P with the observed crystallization kinetics provides a deeper understanding of the microscopic mechanism of crystallization.

Crystallographic effect of a high magnetic field on a solidified hypoeutectic Zn–Al alloy

Hypoeutectic Zn–4.45 wt% Al solidified under a high magnetic field was investigated crystallographically. With the field, the primary zinc-rich β phase is distributed homogeneously and orients with thecaxis perpendicular to the magnetic field direction. These results are attributed to the magnetic viscosity resistance force and the magnetocrystalline anisotropy of zinc, respectively. The orientation modification also leads to a preferential alignment of the flat-shaped primary β dendrites. Furthermore, with the field, the eutectic β phase shows an orientation character similar to that of the primary β phase. This arises from its continuous growth with the primary β phase. In addition, a specific crystallographic orientation relationship ({0001}β||{111}α, 〈1\overline 210〉β||〈110〉α) exists in some of the eutectics (between the eutectic zinc-rich β and aluminium-rich α phases). However, this orientation relationship is related to the distribution of primary β dendrites, which originates from the independent nucleation of the pseudo-primary α phase attached to the primary β dendrites.

亚共晶Zn-4.45%Al合金凝固组织的晶体学特征 *

将亚共晶Zn-A1合金凝固，借助EBSD技术研究了其组织的晶体学特征。结果表明，在样品上部形成了由多个伸长共晶团构成的羽毛状组织，且此共晶团中∥和口相存在取向关系{0001}II{111}〈19-10〉pII〈110〉n。其次，初生卢相沉积在样品下部，且其呈扁平枝晶状：六个一次枝晶臂沿〈lOiO〉方向快速生长而沿〈0001〉方向则生长缓慢。此外，初生卢相内部存在a相析出物，且初生卢与此口也存在上述取向关系，但初生卢与周围的伪初生口及其附近的共晶卢与口之间没有特定取向关系。

Characterisation of Oxide Films in Al-Mg Alloy Melts

Oxide films in Al-0.7Mg and Al-9.4Si-2.3Cu-1.0Zn-0.49Mg (in wt%) alloy melts were characterised using advanced analytical electron microscopy. The oxides were collected by pressurised melt filtration for direct examination by SEM and TEM. The results showed that the oxide films consisted of numerous sub-micron sized oxide particles, rather than continuous solid films. The oxide particles formed in the two Mg-containing alloys were identified as MgAl2O4spinel by selected area electron diffraction (SAED) and high resolution TEM combined with EDS analysis. The low level of Mg in the melt resulted in the change of the oxide from alumina to MgAl2O4spinel. The MgAl2O4crystals were typically faceted with their {1 1 1} crystal planes and were about 0.2-1.2 μm in size. High resolution TEM examination of the MgAl2O4/ a-Al interfaces revealed that there was a cube-on-cube orientation relationship between the two crystals. The possibility of MgAl2O4particles to act as nucleation sites for α-Al grains during solidification is discussed in terms of the lattice matching at the MgAl2O4/ α-Al interfaces along the specific crystallographic orientation relationship.

Oriented kokchetavite compound rods in clinopyroxene of Kokchetav ultrahigh-pressure rocks

Two microdiamond-bearing samples, a dolomite marble and a garnet-clinopyroxene rock, from the Kokchetav ultrahigh-pressure metamorphic terrane were selected in the present study to explore the possible origin of KAlSi3O8 rod inclusions oriented along the c-axis of clinopyroxene host.The KAlSi3O8 rod inclusions at clinopyroxene cores, where K2O content is high in the range of 0.5–1.0wt.%, are mostly fine-grained with a rod width less than 1μm. AEM studies showed that the KAlSi3O8 phase in most rod inclusions is kokchetavite. K-feldspar is present only in a few cases, probably the result of phase transformation/recrystallization from kokchetavite during rock exhumation. Electron diffractions further showed that kokchetavite rods are oriented parallel to clinopyroxene [001] direction and they exhibit the same epitaxial relation with the clinopyroxene host in both samples with the (Al, Si)O4 tetrahedra chains along the hexagonal a-axis of kokchetavite parallel to the single SiO4 chain along the c axis of clinopyroxene; i.e., [12¯10]Ko//[001]Cpx and (0001)Ko//(100)Cpx. It is interesting to note that kokchetavite is always in association with phengite, tremolite, β-cristobalite, Si-rich (Al, K, Ca-bearing) low crystallinity phase, ±Si–Ca (Cl, As) phase, ±calcite, ±apatite, ±lollingite (FeAs2), forming compound rods. Furthermore, all these phases are also present within submicron-scale polyphase inclusion pockets in garnet within garnet-clinopyroxene rock sample. These kokchetavite compound rods are therefore most likely to have resulted from melt/fluid-clinopyroxene interactions leading to epitaxial deposition rather than exsolution sensu stricto from the clinopyroxene host. The suggested melt/fluid would have an “external” and/or an “internal” origin related to rock partial melting involving phengite breakdown.Discrete phlogopite and phengite needle-like inclusions with a needle width less than 1μm, as well as phlogopite–phengite and kokchetavite-mica intergrowth needles, are also not uncommon in clinopyroxene cores. There are specific crystallographic orientation relationships among phases. These micas might have formed earlier than kokchetavite and have exsolved from clinopyroxene host, although the mass balance issue during exsolution and the temporal relation between phlogopite and phengite needles remain to be settled.Clinopyroxene rims generally contain mica needles only. Domains near fractures with coarse-grained kokchetavite compound rods or with coarse-grained phlogopite+quartz needles are not uncommon. These clinopyroxene rims/domains are low in K2O (<0.5wt.%) and their inclusions are most probably a result of precipitation/recrystallization from late-stage(s) infiltrated fluid-clinopyroxene interactions.

A TEM study of the oriented orthopyroxene and forsterite inclusions in garnet from Otrøy garnet peridotite, WGR, Norway: new insights on crystallographic characteristics and growth energetics of exsolved pyroxene in relict majoritic garnet

AbstractRegularly oriented orthopyroxene (opx) and forsterite (fo) inclusions occur as opx + rutile (rt) or fo + rt inclusion domains in garnet (grt) from Otrøy peridotite. Electron diffraction characterization shows that forsterite inclusions do not have any specific crystallographic orientation relationships (COR) with the garnet host. In contrast, orthopyroxene inclusions have two sets of COR, that is, COR‐I: &lt;111&gt;grt//&lt;001&gt;opx and {110}grt∼//∼{100}opx (∼13° off) and COR‐II: &lt;111&gt;grt//&lt;011&gt;opx and {110}grt∼//∼{100}opx (∼14° off), in four garnet grains analysed. Both variants of orthopyroxene have a blade‐like habit with one pair of broad crystal faces parallel/sub‐parallel to {110}grt plane and the long axis of the crystal, &lt;001&gt;opx for COR‐I and &lt;011&gt;opx for COR‐II, along &lt;111&gt;grt direction. Whereas the lack of specific COR between forsterite and garnet, along with the presence of abundant infiltrating trails/veinlets decorated by fo + rt at garnet edges, provide compelling evidence for the formation of forsterite inclusions in garnet through the sequential cleaving–infiltrating–precipitating–healing process at low temperatures, the origin of the epitaxial orthopyroxene inclusions in garnet is not so obvious. In this connection, the reported COR, the crystal habit and the crystal growth energetics of the exsolved orthopyroxene in relict majoritic garnet were reviewed/clarified. The exsolved orthopyroxene in a relict majoritic garnet follows COR‐III: {112}grt//{100}opx and &lt;111&gt;grt//&lt;001&gt;opx. Based on the detailed trace analysis on published SEM images, these exsolved orthopyroxene inclusions are shown to have the crystal habit with one pair of broad crystal faces parallel to {112}grt//{100}opx and the long crystal axis along &lt;111&gt;grt//&lt;001&gt;opx. Such a crystal habit can be rationalized by the differences in oxygen sub‐lattices of both structures and represents the energetically favoured crystal shape of orthopyroxene inclusions in garnet formed by solid‐state exsolution mechanism. Considering the very different COR, crystal habit, as well as crystal growth direction, the orthopyroxene inclusions in garnet of the present sample most likely had been formed by mechanism(s) other than solid‐state exsolution, regardless of their regularly oriented appearance in garnet and the COR specification between orthopyroxene and garnet. In fact, the crystallographic characteristics of orthopyroxene and the similar chemical compositions of garnet at opx + rt inclusion domains, fo + rt inclusion domains/trails and garnet rim suggest that the orthopyroxene inclusions in the garnet are most likely formed by similar cleaving‐infiltration process as forsterite inclusions, though probably at an earlier stage of metamorphism. This work demonstrates that the oriented inclusions in host minerals, with or without specific COR, can arise from mechanism(s) other than solid‐state exsolution. Caution is thus needed in the interpretation of such COR, so that an erroneous identification of exhumation from UHP depths would not be made.

Biepitaxial Growth of High-Quality Semiconducting NiO Thin Films on (0001) Al2O3 Substrates: Microstructural Characterization and Electrical Properties

This paper reports the effects of substrate temperature on the microstructural characteristics and electrical properties of p-type semiconducting NiO thin films grown on (0001) Al2O3 substrates. NiO thin films were biepitaxially grown on (0001) Al2O3 substrates by radiofrequency magnetron sputtering, and they showed specific crystallographic orientation relationships: [110]NiO∥[0110]Al2O3, [112]NiO∥[2110]Al2O3 (in-plane), and [111]NiO∥[0001]Al2O3 (out-of-plane). Thus, a low lattice mismatch of 7.52% was obtained between the NiO thin films and the (0001) Al2O3 substrates. The film grown at 600 °C consisted of cubic and rhombohedral NiO grains, while the NiO thin films grown at substrate temperature below 400 °C only consisted of cubic NiO grains. Atoms at the grain boundaries between the cubic and the rhombohedral NiO grains perfectly coincided with each other because of the same atomic stacking sequences along [111]c-NiO and [0003]r-NiO and with equal interatomic distances. Further, the paper d...