Search

In restorative dentistry, dental composites have become a popular material of choice due to the increasing aesthetic demands and address challenges like recurrent cavities and restorative bulk fracture, which are the most common causes of dental composite failure. To address these issues, various types and shapes of reinforcement fillers were researched to enhance the mechanical properties of composite formulations over conventional composites. Furthermore, antibacterial agents and ion-releasing fillers are used to prevent secondary caries and promote the remineralisation of dental tissue. This review article aims to review the literature of dental resin composites, focusing on various filler categories and their impact on the materials' performance, to aid future development of dental resin composites for clinical applications with optimal properties that can overcome current limitations.

Fused Filament Fabrication (FFF) is a popular additive manufacturing process for creating prototypes and end-use products. Infill patterns, which fill the interior of hollow FFF-printed objects, play a crucial role in determining the mechanical properties and structural integrity of hollow structures. This study investigates the effects of infill line multipliers and different infill patterns (hexagonal, grid, and triangle) on the mechanical properties of 3D printed hollow structures. Thermoplastic poly lactic acid (PLA) was used as the material for 3D-printed components. Infill densities of 25%, 50%, and 75% were chosen, along with a line multiplier of one. The results indicate that the hexagonal infill pattern consistently demonstrated the highest Ultimate Tensile Strength (UTS) of 1.86 MPa across all infill densities, out-performing the other two patterns. To maintain a sample weight below 10 g, a two-line multiplier was utilised for a 25% infill density sample. Remarkably, this combination exhibited a UTS value of 3.57 MPa, which is comparable to samples printed at 50% infill density, which were 3.83 MPa. This research highlights the importance of line multiplier in combination with infill density and infill pattens to ensuring the achievement of the desired mechanical properties in the final product.

Carbon nanotubes (CNTs) have been applied as nano-fillers to improve mechanical, thermal and electrical properties of polymers. Despite near net shape techniques could be used to manufacture nanocomposites, micromachining processes are still necessary to attain high surface quality and dimensional accuracy. Besides, micromachining of nanocomposites could be a potential approach to produce micro-features/components, following the miniaturisation trend of modern manufacturing. Therefore, micro-machining of these relatively new materials needs to be investigated. A comprehensive investigation on machinability of nanocomposites will be presented in terms of chip formation, cutting force, tool wear, surface morphology and surface roughness. Three controlled quantitative factors are investigated at different levels, including filler loading, cutting speed and feed per tooth (FPT). Micro-slotting is performed on an ultra-precision desktop micro-machine tool using uncoated carbide micro-end mill. The additions of multi-walled carbon nanotube (MWCNT) have shown significant effects on the machinability of these epoxy-based nanocomposites including a dramatic reduction in cutting force and machined surface roughness with accelerating tool wear compared with a neat polymer. The irregular cutting force variations when micro-milling epoxy/MWCNT nanocomposites at feed rates below minimum uncut chip thickness (MUCT) (lower than 2 μm) indicating by their fluctuations that different from those in higher feed rates. It possibly shows the impact of size effects that are illustrated by the observations of chip formation, surface morphology, cutting force profiles as well as specific cutting energy calculation.

Nanomaterials such as graphene have been added to various matrices to enhance mechanical, thermal and electrical properties for various applications requiring intricate designs at the micro-scale. At this scale, mechanical micro-machining is utilised as post-processing to achieve high surface quality and dimensional accuracy while still maintaining high productivity. Therefore, in this study, the machinability of polymer nanocomposites in micro-scale (micro-machinability) is investigated. Graphene (0.3 wt%)-reinforced epoxy nanocomposites were fabricated using traditional solution mixing and moulding. The samples were then subjected to micro-milling at various cutting speeds using three different micro-tools, including uncoated, diamond and diamond-like carbon (DLC) tools. Mechanical and thermal properties of nanocomposite were also used to support the discussions. The result indicates that the DLC-coated tool shows better performance than the other tools for less tool wear, improved surface quality and less cutting forces.

A low temperature fired Na2CaV4O12 ceramic was synthesized via a solid-state reaction route at a temperature range of 350–550 °C. The Thermal analysis confirmed the densification and melting temperature of Na2CaV4O12 to be 530 °C and 580 °C, respectively. Dielectric properties together with the electrical conductivity were characterized at a broad frequency and temperature range. A super-low relative permittivity of er = 7.72 and loss tangent of tanδ = 0.06 were obtained at 1 MHz at room temperature. A dielectric anomaly peak took place around 515 °C, which was associated with the phase transition from P4/nbm to P 4 ¯ b2. Ac impedance spectrum coupled with complex modulus plots unveiled the electrical conduction mechanism, which was dominated by the short-range movement of the charge carriers at low temperatures (T ≤ 220 °C) however long-range migration of charge carriers emerged at higher temperatures.

Solution blow spinning (SBS) technique can produce nanofibers (NFs) mat in large-scale production. In this work, the SBS was used to fabricate piezoelectric polyvinylidene fluoride (PVDF) NF membranes that can be utilized for energy harvesting applications. The effect of operating air pressure from (2–5 bar) on the surface morphology of the NFs has been studied. The structural analysis for crystalline polymorph β-phase for PVDF powder, casted film, electrospinning and SBS NFs has also been presented with the aid of Fourier-transform infrared spectroscopy and X-ray diffraction (XRD). Piezoelectric characteristics of PVDF NFs mats were tested by applying impact impulse with different weights from different heights between 1 and 10 cm. The sensitivity of the voltage response increased from 1.71 mV/g to 8.98 mV/g, respectively. Besides, the SBS generated PVDF mat is found to be sensitive to pressure forces in a range of few Newtons with the generated voltage according to detected sensitivity of 80 mV/N based on the analysis of the impact of a few Hertz mechanical vibrations. In addition, the produced SBS NFs were applied as an acoustic signal detector within different acoustic frequencies. The results suggest that the β-phase PVDF nanofibrous membrane produced via the SBS technique has a great potential to be used as a piezoelectric sensor.

Effect of order/disorder transition on microwave dielectric characteristics is reported to develop a deeper understanding of structure-property relationship in spinel ceramics. Dense xLi4/3Ti5/3O4-(1-x)Mg2TiO4 (0.6≤x≤0.9) spinel ceramics were synthesized and characterized for structural and dielectric properties. The critical order/disorder structural transition was induced when x < 0.8, resulting in the ceramic crystallized into a primary cubic spinel phase, while when x > 0.8, the ceramic crystallized into a disordered face-centered cubic phase. The cation occupation caused this order-disorder transition, which directly influenced the variation in microwave dielectric properties. At x = 0.75 the maximum degree of order was achieved resulting in a maximum quality factor of 55,000 GHz and a near-zero τf = 2.9 ppm/oC. Dielectric properties decreased sharply after x = 0.8 when the disorder face-centered cubic phase started to crystallize. All the results indicated that cation ordering/disordering plays a critical role in determining the optimum microwave dielectric properties in spinel ceramics.

At extremely low temperatures, Ag2CaV4O12 was easily synthesized using the traditional solid-state approach. With a low relative permittivity (εr) of 7.52, a high quality factor (Q × f) of 48 800 GHz (f = 13.6 GHz), and a temperature coefficient of resonance frequency (τf) of −77.4 ppm/°C, dense ceramics sintered at 480 °C with outstanding microwave dielectric characteristics were attained. By combining with rutile TiO2, a composite ceramic with balanced microwave dielectric properties (τf = 3.2 ppm/°C, εr = 10.96, and Q × f = 49 081 GHz) was achieved. No chemical reaction between Ag2CaV4O12 and silver and aluminum occurred. All of the findings show that Ag2CaV4O12 has the potential to be used as dielectric resonances in wireless communication and as substrates in low-temperature cofired ceramics. Furthermore, the processing at an ultralow temperature of Ag2CaV4O12 shows that it is extraordinarily energy saving from the point of view of fabrication and might allow for room-temperature synthesis by combining with high-energy mechanical milling or sintering using a high pressure such as hot isostatic pressing (HIP), spark plasma sintering (SPS), and cold sintering (CS).

Three-dimensional printing-based additive manufacturing has emerged as a new frontier in materials science, with applications in the production of functionalized polymeric-based hybrid composites for various applications. In this work, a novel conceptual design was conceived in which an AC electric field was integrated into a commercial 3D printer (-based fused filament fabrication (FFF) working principle) to in situ manufacture hybrid composites having aligned ceramic filler particles. For this work, the thermoplastic poly lactic acid (PLA) was used as a polymer matrix while 10 vol% KNLN (K0.485Na0.485Li0.03NbO3) ceramic particles were chosen as a filler material. The degree of alignment of the ceramic powders depended upon print speed, printing temperature and distance between electrodes. At 210 °C and a 1 kV/mm applied electric field, printed samples showed nearly complete alignment of ceramic particles in the PLA matrix. This research shows that incorporating electric field sources into 3D printing processes would result in in situ ceramic particle alignment while preserving the other benefits of 3D printing.

Adjustment on resonance frequency stability against the sintering temperature of Sr3V2O8 was realized by adjusting the Sr:V mole ratio. Effects of Sr:V ratio on sintering behavior and dielectric properties of Sr3V2O8 were studied. The sintering temperature was sucessfully reduced to 950°C from 1150°C. With increasing vanadium content, both relative permittivity and quality factor decreased, while the temperature coefficient of resonance frequency shifted from positive to negative values. Especially, a near‐zero τf of −1.1 ppm/°C along with a low permittivity (εr) of 9.8 and a quality factor Q × f of 24 120 GHz was successfully achieved in Sr3‐yV2O8‐y ceramic (y = 0.6, sintered at 950°C). The wide compositional and processing adjustment window, favorable dielectric performances, and good chemical compatibility with silver render Sr3‐yV2O8‐y ceramics potential candidates in multilayer electronic devices.

As one of the candidates of low-temperature cofired ceramics (LTCC), the sintering behavior, dielectric properties, and silver chemical compatibility of NaCaVO4 were studied. The bulk ceramic samples were densified well at a low sintering temperature of 720 oC with an optimal bulk density of 2.87 g/cm3. Excellent microwave dielectric properties with a low relative permittivity er ~ 9.9, a high quality factor Q × f ~ 31,600 GHz, and a temperature coefficient of resonance frequency τf ~ -66.5 ppm/°C were achieved at 11.5 GHz. The far infrared reflectivity spectra revealed the intrinsic dielectric properties (relative permittivity of 8.34 and dielectric loss of 2.7×10-4) are comparable to the measured values. The absence of chemical reaction between NaCaVO4 and silver at firing temperature, evidenced by X-ray diffraction and energy dispersive spectroscopy indicated the potential prospect for LTCC application. Furthermore, the very low density of NaCaVO4 opens up an avenue for its potential applications in light-weight devices.

Solution blow spinning (SBS) is gaining popularity for producing fibres for smart textiles and energy harvesting due to its operational simplicity and high throughput. The whole SBS process is significantly dependent on the characteristics of the attenuation force, i.e., compressed air. Although variation in the fibre morphology with varying air input pressure has been widely investigated, there is no available literature on the experimentally determined flow characteristics. Here, we have experimentally measured and calculated airflow parameters, namely, output air pressure and velocity in the nozzle wake at 12 different pressure values between 1 and 6 bar and 11 different positions (retracted 5 mm to 30 mm) along the centreline. The results obtained in this work will answer many critical questions about optimum protrusion length for the polymer solution syringe and approximate mean fibre diameter for polyvinylidene fluoride (PVDF) at given output air pressure and velocity. The highest output air pressure and velocity were achieved at a distance of 3–5 mm away from the nozzle wake and should be an ideal location for the apex of the polymer solution syringe. We achieved 250 nm PVDF fibres when output air pressure and velocity were 123 kPa and 387 m/s, respectively. Published version

Ceramic matrix composites (CMCs) are a class of composite materials in which filler are incorporated within a ceramic matrix. As a result of filler addition to ceramic matrix, specific properties can be altered. There are various ways to manufacture ceramics and CMCs, mainly depending upon the filler material and the final application. One such property is a reduction in crack propagation. Although their constituents are brittle, CMCs have found their applications in the vast majority of the area, including space, refractories, energy storage, and automotive. This chapter considers classification and manufacturing CMCs. This chapter summarises state of the art for CMCs and their manufacturing techniques and lays the foundation for their micromachining.

Borates are promising candidates as dielectric substrate materials in low temperature cofired ceramics technology (LTCC) due to their relative low sintering temperatures and relative permittivities compared to their counterparts. However, synthesizing borates having single-phase is still challenging because of the volatility and hydrophilicity of boron resources. In this work, a compositional design was utilized to synthesize single-phase LiBGeO4 ceramics over a broad temperature range from 600 to 840 °C. Radio-frequency dielectric behaviours featured a strong temperature dependence, especially at high temperatures (>400 °C), which is related to the thermally activated polarizations. LiBGeO4 ceramic sintered at 820 °C has optimum microwave dielectric properties with the relative permittivity (er) of 6.28, a quality factor (Q × f) of 21,620 GHz, and a temperature coefficient of resonance frequency (τf) of -88.7 ppm/°C. LiBGeO4 also showed chemical inertness when cofired with silver (Ag), provided an evidence for its utilization in LTCC technology. Overall, this work provides a strategy for facile synthesis of phase pure borates, via the proposed two-step process to obtain stable boron resources.

Polyvinylidene fluoride (PVDF)-based piezoelectric materials (PEMs) have found extensive applications in energy harvesting which are being extended consistently to diverse fields requiring strenuous service conditions. Hence, there is a pressing need to mass produce PVDF-based PEMs with the highest possible energy harvesting ability under a given set of conditions. To achieve high yield and efficiency, solution blow spinning (SBS) technique is attracting a lot of interest due to its operational simplicity and high throughput. SBS is arguably still in its infancy when the objective is to mass produce high efficiency PVDF-based PEMs. Therefore, a deeper understanding of the critical parameters regarding design and processing of SBS is essential. The key objective of this review is to critically analyze the key aspects of SBS to produce high efficiency PVDF-based PEMs. As piezoelectric properties of neat PVDF are not intrinsically much significant, various additives are commonly incorporated to enhance its piezoelectricity. Therefore, PVDF-based copolymers and nanocomposites are also included in this review. We discuss both theoretical and experimental results regarding SBS process parameters such as solvents, dissolution methods, feed rate, viscosity, air pressure and velocity, and nozzle design. Morphological features and mechanical properties of PVDF-based nanofibers were also discussed and important applications have been presented. For completeness, key findings from electrospinning were also included. At the end, some insights are given to better direct the efforts in the field of PVDF-based PEMs using SBS technique. Published version

Micromachining of nanocomposites is deemed to be a complicated process due to the anisotropic, heterogeneous structure, and advanced mechanical properties of these materials associated with the size effects in micromachining. It leads to poorer machinability in terms of high cutting force, low surface quality, and high rate of tool wear. In part 1 of this two-part review paper, a comprehensive review on mechanical properties of various nanocomposites will be presented while the second part of the paper will focus on the micro-machinability of these nanocomposite materials.

Micromachining of nanocomposites is deemed to be a complicated process due to the anisotropic, heterogeneous structure and advanced mechanical properties of these materials associated with the size effects in micromachining. It leads to poorer machinability in terms of high cutting force, low surface quality, and high rate of tool wear. A comprehensive review on mechanical properties of nanocomposites aiming to pointout their effects on micro-machinability has been addressed in part 1. In part 2, the subsequent micro-machining processes are critically discussed based on relevant studies from both experimental and modeling approaches. The main findings and limitations of these micro-machining methods in processing nanocomposites have been highlighted together with future prospects.

Computational fluid dynamics (CFD) was used to investigate characteristics of high-speed air as it is expelled from a solution blow spinning (SBS) nozzle using a k-&epsilon, turbulence model. Air velocity, pressure, temperature, turbulent kinetic energy and density contours were generated and analysed in order to achieve an optimal attenuation force for fibre production. A bespoke convergent nozzle was used to produce polyvinylidene fluoride (PVDF) fibres at air pressures between 1 and 5 bar. The nozzle comprised of four parts: a polymer solution syringe holder, an air inlet, an air chamber, and a cap that covers the air chamber. A custom-built SBS setup was used to produce PVDF submicron fibres which were consequently analysed using scanning electron microscope (SEM) for their morphological features. Both theoretical and experimental observations showed that a higher air pressure (4 bar) is more suitable to achieve thin fibres of PVDF. However, fibre diameter increased at 5 bar and intertwined ropes of fibres were also observed.

Alkaline earth metal vanadates have drawn attention because of their potential applications in electrochemical devices. Here, Na2CaV4O12 was prepared at extremely low temperatures (350–550 °C) and showed a semiconductor behavior with a bandgap of 2.92 eV. A phase transition from P4/nbm to P 4 b2 occurred at 510 °C was identified by an in-situ XRD upon heating, where the 16 n site for oxygen atoms in the P4/nbm phase evolves into two distinguishable 8i sites in the P 4 b2 phase. Ionic conduction in Na2CaV4O12 at elevated temperatures was reported for the first time in the present work. A strong correlation between ionic conductivity and phase structure of Na2CaV4O12 is observed. The charged carriers are mainly sodium ions for the low-temperature P4/nbm phase, while mixed conduction contributed by sodium ions and oxide ions happened in the transformed phase. Bond valence-based energy landscape calculations disclosed a two-dimensional interstitial diffusion mechanism for Na+ ions in the Na2Ca-layers, as well as a two-dimensional diffusion mechanism for oxide ions in the V4O12-layers. The novel semiconductor ceramic would have potential applications in all-solid sodium ions batteries or solid oxide fuel cells as electrolytes.

Low-firing and temperature stable microwave dielectric ceramics of Ba2LnV3O11 (Ln = Nd, Sm) were prepared by solid-state reaction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the phase purity, crystal structure, sintering behavior, and microstructure. The XRD patterns indicated that Ba2LnV3O11 (Ln =Nd, Sm) ceramics belong to monoclinic crystal system with P21/c space group in the whole sintering temperature range (800-900 °C). Both ceramics could be well densified at 880 °C for 4 h with relative densities higher than 96%. The Ba2LnV3O11 (Ln =Nd, Sm) samples sintered at 880 °C for 4 h exhibited excellent microwave dielectric properties: er = 12.05, Q×f = 23,010 GHz, τf = –7.7 ppm/oC, and er = 12.19, Q×f = 27,120 GHz, τf = –16.2 ppm/oC, respectively. Besides, Ba2LnV3O11 (Ln =Nd, Sm) ceramics could be well co-fired with the silver electrode at 880 °C. This article is protected by copyright. All rights reserved.

Highly flexible lead free composite film having random distribution of ceramic filler was synthesized using Barium Titanate (BT) as a filler and inexpensive Thermoplastic Polyurethane (TPU) as a matrix. The results show that the 30 vol% BT-TPU composite has a dielectric constant of ~31 which is comparable to the expensive and difficult to produce PVDF based composites. With a breakdown field of 150 kV/mm, an energy density value of ~3 J/cm3 was estimated. These lead-free TPU based composites provide an alternative to PVDF based composites for energy storage applications.

Phase formation, crystal structure and dielectric properties of NaCa4V5O17 ceramics fabricated via a solid state reaction route at relatively low temperatures (780–860 °C) were investigated. NaCa4V5O17 crystallizes in a triclinic structure. Dielectric properties were measured based on the Hakki-Coleman post resonator method at microwave frequency. Specially, a specimen sintered at 840 °C demonstrated balanced dielectric properties with a permittivity er = 9.72, a quality factor Q×f = 51,000 GHz, and a temperature coefficient of resonance frequency τf = −84 ppm/°C. NaCa4V5O17 ceramics showed excellent chemical compatibility with Ag metal electrodes. Besides, the thermal stability of resonance frequency was effectively adjusted through formation of composite ceramics between NaCa4V5O17 and TiO2 and a near-zero τf ˜ 1.3 ppm/°C accompanied with er = 14.9 and Q×f = 19,600 GHz was achieved when 50% mol TiO2 was added. All the merits render NaCa4V5O17 a potential candidate for multilayer electronic devices.

The availability of carbyne in carbon nanotubes (CNTs) induces intrinsic stiffening and strengthening of CNTs, and is exploited for the very first time in this report to process epoxy nanocomposites with improved mechanical and electrical properties. The existence of encapsulated carbyne in double wall CNTs (DWNTs) was confirmed using High Resolution Transmission Electron Microscopy (HR-TEM). The intrinsic stiffening of carbyne reinforced DWNTs (c-DWNTs) in epoxy matrix was visually confirmed by Field Emission Scanning Electron Microscopy (FE-SEM). In comparison to raw DWNTs reinforced epoxy nanocomposites, c-DWNTS imparted modest but improved tensile strength (5.6%), elastic modulus (9.7%), failure strain (9.9%) and fracture toughness (13%) to their respective epoxy nanocomposites. This inaugural study on carbyne-filled polymer composites also reports a minor but distinct increase (an order of magnitude) in the electrical conductivity for c-DWNTs filled epoxy nanocomposites compared to DWNT filled epoxy nanocomposites.

Piezoelectric composites made from soft and hard lead zirconium titanate (PZT) particles as filler and an epoxy as the matrix were prepared by dielectrophoresis and studied for their piezoelectric properties. It was found that the dielectric constant of the piezoelectric filler plays a significant role in determining the final piezoelectric properties of the composites. Composites with lower dielectric constant for the PZT filler material showed better piezoelectric properties compared to the composites with high dielectric constant filler. This can be ascribed to a more efficient poling of the piezoelectric filler particles. The aging behaviour of these composites was compared to that reported for monolithic ceramics.

A Ca5Ni4(VO4)6 low loss microwave dielectric ceramic with A site deficient garnet structure was prepared via the conventional solid state reaction method. Ca5Ni4(VO4)6 sintered at 980 °C for 4 h to a relative density of 96.2% exhibits favorable microwave dielectric properties such as a permittivity of 10.9, a Q×f value of 96,500 GHz, and a τf value of −63.6 ppm/°C. Its large negative τf could be compensated by forming a solid solution with LiCa2Mg2V3O12, that led to improved properties with a near-zero τf=−3.7 ppm/°C, er=10.2, Q×f=59,300 GHz for 0.8Ca5Ni4(VO4)6−0.2LiCa2Mg2V3O12 after sintering at 955 °C for 4 h. Further on, 0.8Ca5Ni4(VO4)6−0.2LiCa2Mg2V3O12 proved to be chemically compatible with Ag electrodes, so it might be a possible candidate for LTCC applications.

A Li4WO5 ceramic with rock salt structure was prepared by the solid-state reaction method and its microwave dielectric properties was demonstrated for the first time. It could be well densified at relatively low sintering temperature (∼890 °C). XRD and DTA analysis revealed a phase transformation from cubic to orthorhombic occured at 700 °C. Excellent microwave dielectric properties with a near-zero temperature coefficient of resonant frequency ∼−2.6 ppm/°C, a relative permittivity ∼8.6 and a quality factor ∼23,100 GHz (at 11.0 GHz) was obtained. Li4WO5 was found to be chemically compatible with silver powders when sintered at 890 °C. All the results indicate that the Li4WO5 ceramic is a promising candidate as a base material in low temperature cofired ceramic technology.

A cost-effective and rapid mechanical alloying method was used to prepare Yb-stuffed and Te-substituted CoSb3 to study the thermoelectric properties of this material. Yb rattles inside the cage-like structure of CoSb3 which effectively reduces the phonon mean free path and results in a lattice thermal conductivity comparable to those of costly nanostructured CoSb3 materials. A very low lattice thermal conductivity of 1.17 W m−1 K−1 at ∼550 K was obtained. A zT value of ∼0.7 was reported at 600 K due to the very low lattice thermal conductivity.

Bi2Te3 based alloys play a dominant role in commercial applications in the fields of thermoelectric energy generation and solid state cooling. By combining the densification of nanostructured powders followed by a two-step hot forging process, hierarchical nanostructured p-type Bi0.5Sb1.5Te3 alloys with good preferred orientation were successfully fabricated. The Seebeck coefficient in the direction perpendicular to the pressing force, which is highly anisotropic, is much greater than that of the material sintered via one-step sintering. Meanwhile, the nanostructure and crystal defects produced during hot forging also contribute to both higher Seebeck coefficient, and lower thermal conductivity due to more effective and preferential scattering of phonons than electrons. As a result, a 50% enhancement of ZT value (from 1 to above 1.5) in the orientated, hierarchical, nanostructured alloys was obtained.

Atomic-scale percolation phenomena of electric and thermal conductivity were found in digenite CuxS. Copper ions are randomly located between the closely packed sulphur ions and jump to another position via unoccupied interstices. Near the percolation threshold value (fc ∼ 0.3) in the conductive region, a 60% enhancement of ZT value can be obtained. This indicates that the percolation phenomena can provide a new strategy to optimize the properties of thermoelectric materials, especially for quasi disordered materials.

Graphene was prepared using liquid phase exfoliation and dispersed in an alumina matrix using an ultrasonication and powder processing route. Al 2 O 3 –graphene composites with up to 5 vol% content were densified (>99%) using SPS. The fracture toughness of the material increased by 40% with the addition of only 0.8 vol% graphene. However for higher graphene contents the improvement in fracture toughness was limited. Graphene changed the mechanism of crack propagation for the alumina matrix from inter-granular to trans-granular. The formation of an inter-connecting graphene network promoted easy fracture for concentration ⩾2 vol%. Elastic modulus remained nearly constant for up to 2 vol% and decreased significantly for 5 vol% due to the formation of the inter-connecting graphene network. Fracture toughness measured with the indentation and chevron notch methods were consistent up to 2 vol% and at 5 vol% the percolating network of graphene resulted in easy crack propagation with significant discrepancy between the results for the two methods.

Different morphologies (worm-like, straight and twisted) of multiwalled carbon nanotubes (MWCNT) are synthesized by carefully controlling the C2H2 flow rate. Unique mixed ferrite nanoparticles were synthesized and characterized as the appropriate catalyst for the growth of MWCNT. Scanning electron microscope and transmission electron microscope was extensively used to explore the morphological and structural properties. Electrical properties of MWCNT suggest semiconducting behavior. Infrared (IR) radiation detection is demonstrated using MWCNT and prototypes of room temperature and low temperature. IR radiation detectors have been made using different morphologies of MWCNT as the active sensor material.

The effect of substitution and oxidation-reduction on the thermal conductivity of perovskite-like layered structure (PLS) ceramics was investigated in relation to mass contrast and non-stoichiometry. Sr (acceptor) was substituted on the A site, while Ta (donor) was substituted on the B site of La2Ti2O7. Substitution in PLS materials creates atomic scale disorders to accommodate the non-stoichiometry. High resolution transmission electron microscopy and X ray diffraction revealed that acceptor substitution in La2Ti2O7 produced nanoscale intergrowths of n = 5 layered phase, while donor substitution produced nanoscale intergrowths of n = 3 layered phase. As a result of these nanoscale intergrowths, the thermal conductivity value reduced by as much as ∼20%. Pure La2Ti2O7 has a thermal conductivity value of ∼1.3 W/m K which dropped to a value of ∼1.12 W/m K for Sr doped La2Ti2O7 and ∼0.93 W/m K for Ta doped La2Ti2O7 at 573 K.

In 0.95[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.05CaTiO3 ceramics, the temperature TS (dielectric permittivity shoulder at about 125 °C) represents a transition between two different thermally activated dielectric relaxation processes. Below TS, the approximately linear decrease of the permittivity with the logarithm of frequency was attributed to the presence of a dominant ferroelectric phase. Above TS, the permittivity shows a more complicated dependence of the frequency and Raman modes indicate a sudden increase in the spatial disorder of the material, which is ascribed to the presence of a nonpolar phase and to a loss of interaction between polar regions. From 30 to 150 °C, an increase in the maximum polarization with increasing temperature was related to three possible mechanisms: polarization extension favoured by the simultaneous presence of polar and non-polar phases; the occurrence of electric field-induced transitions from weakly polar relaxor to ferroelectric polar phase; and the enhanced polarizability of the crystal structure induced by the weakening of the Bi-O bond with increasing temperature. The occurrence of different electric field induced polarization processes with increasing temperature is supported by the presence of additional current peaks in the current-electric field loops.

Disordered layered p-type bismuth telluride was obtained by high pressure (1 GPa) and high strain deformation along the c-axis direction of commercially available single crystals. After initial deformation the p-type bismuth telluride flakes were subsequently fully densified by cold pressing (800 MPa at room temperature). As a result of the severe plastic deformation, the samples showed highly anisotropic electrical and thermal conductivities. In particular, the thermal conductivity measured along the pressing direction was as low as 0.34 W m−1 K−1, which is one of the lowest values reported for fully dense p-type bismuth telluride. The full set of thermoelectric properties of the disordered bismuth antimony telluride is critically discussed.