1. Overview of Advanced Functional Ceramics

Concept: Advanced functional ceramics are materials that exhibit various properties—such as electrical, magnetic, optical, acoustic, thermal, and mechanical characteristics—and their cross-coupling effects. These include piezoelectric, magnetoelectric, thermoelectric, and photoelectric materials capable of energy conversion.

Types:

• Electronic ceramics

• Magnetic ceramics

• Sensitive ceramics

• Optical ceramics

• Bioceramics

• Fast ion conductors

• High-temperature superconducting ceramics

Currently, the largest segment of the functional ceramics industry focuses on information functional ceramics or electronic ceramics used in advanced components. These primarily include:

• Dielectric ceramics (electrical insulation ceramics and capacitor ceramics)

• Ferroelectric ceramics

• Piezoelectric ceramics

• Microwave ceramics

• Semiconductor-sensitive ceramics

• Magnetic ceramics

Applications:

A large category of passive devices based on advanced functional ceramics is widely applied in high-tech fields such as electronic information, automatic control, aerospace, marine ultrasound, energy and environment, as well as defense and military industries.

Significance:

Advanced functional ceramics have become a key material for the next generation of electronic components, serving as a source and leader in major innovations in information technology. They are an active research field for technological innovation and high-tech development, and their importance is second only to integrated circuits. This sector represents one of the most competitive and rapidly growing foundational and strategic industries worldwide.

These materials are also an important indicator of a nation’s comprehensive national power and international competitiveness.

Development Trends of Advanced Functional Ceramics:

• Thin film technology

• Low-dimensional materials

• Multiphase materials

• Multifunctionality

• Texturing

• Single crystal structures

• Large sizes, high uniformity, high integrity

• Low-cost production

• Low-temperature synthesis

• Environmental coordination

Development Trends of New Electronic Components:

• High-frequency applications

• Chip-based components

• Miniaturization

• Thin form factors

• Low power consumption

• Fast response rates

• High resolution and precision

• High power

• Multifunctionality

• Composite materials

• Modularization

• Smart and green technologies

• The invention of barium titanate marked a major milestone in functional ceramics.

• Before the 1940s, all dielectrics, including ceramic dielectrics, had a dielectric constant of no more than 80.

• The discovery of high-dielectric ceramic materials based on barium titanate increased the dielectric constant of ceramics by nearly three orders of magnitude.

• These materials were quickly applied to produce high-capacity capacitors for all frequency bands, including microwave frequencies.

• By the latter half of the 20th century, barium titanate-based ceramic dielectric materials underwent rapid development, forming a scaled industry producing various ceramic capacitors for diverse applications.

• The late 1940s saw the development of barium titanate, followed by lead zirconate titanate ceramics in the 1950s.

• These materials were soon used for energy conversion and in various hydroacoustic, ultrasonic, and electroacoustic transducers.

• The introduction of piezoelectric ceramics solidified the position of functional ceramics within the field of inorganic new materials.

• In the 1970s, the successful development of ceramics with positive temperature coefficient (PTC) and negative temperature coefficient (NTC) marked a new era.

• Ceramic materials were no longer limited to being traditional insulating materials but became active components in electronic applications.

• Advances in ferroelectric theory and its applications—such as ferroelectric memory, infrared pyroelectric sensors, and photoelectric effects—ushered in a new phase of innovation.

• Ferroelectric ceramics emerged as a distinct class of functional ceramics.

• Beginning in the 1980s, research into phase transformation and superconductivity broadened the scope of functional ceramics.

• Significant progress was also made in the development of ceramics with exceptional hardness, ultra-high strength, high thermal resistance, and high transparency to light and certain types of radiation.

3. Classification and Applications of Functional Ceramics

Ceramic capacitors are the most widely used type of capacitors in electronic technology. Their primary components include rutile, barium titanate, barium strontium titanate, lead titanate, stannate, and zirconate.

Their structures include disc-type high-voltage ceramics, grain boundary layer capacitors, and multilayer ceramic capacitors (MLCC).

MLCCs (Multilayer Ceramic Capacitors) are a crucial electronic component widely used in various surface-mounted circuits in electronic information products. The primary development directions for MLCCs include high capacity, thin layers, low cost, and high reliability.

Key Materials and Applications:

• Ceramic Dielectric Materials: These are critical in determining the performance of MLCCs. Barium titanate ferroelectric ceramics are the mainstream material.

• Lead Zirconate Titanate (PZT): Predominantly used in ultrasonic transducers, piezoelectric resonators, filters, micro-displacers, and piezoelectric actuators.

• Lead-Free Piezoelectric Ceramics: Recently, lead-free piezoelectric ceramics have gained attention as environmentally friendly materials. These are mainly based on titanates, niobates, and zincates, and are considered high-frequency, low-loss, and temperature-stable dielectric materials.

Applications in Microwave Communications:

• Used in microwave resonators, filters, oscillators, phase shifters, capacitors, antennas, and substrates, playing a crucial role in mobile communications, satellite communications, GPS, Bluetooth, WLAN, and other modern microwave communication technologies.

• Compared to metal cavity resonators, microwave dielectric resonators offer smaller size, lighter weight, better temperature stability, and lower costs, making them essential for miniaturized and integrated communication devices.

Materials for Functional Ceramics:

• High-voltage ceramics, ceramic components, substrates, and multilayer ceramic packaging materials are essential in electronics, microelectronics, and optoelectronics. These include talc ceramics, mullite ceramics, corundum ceramics, alumina, and aluminum nitride.

• Composition: BaTiO3, SrTiO3, MgTiO3, SiC, ZnO, Bi2O3, SnO2, MgCr2O4, etc.

Applications in Sensors and Magnetic Devices:

• Functional ceramics are used in temperature-sensitive, pressure-sensitive, light-sensitive, gas-sensitive, and humidity-sensitive components and sensors.

• They are the base materials for various magnetic and inductive devices, including soft ferrites, permanent magnets, and nanocrystalline soft magnetic alloys. Key examples include manganese-zinc ferrites, nickel-zinc ferrites, and neodymium-iron-boron rare earth permanent magnets.

High-Frequency Devices:

• Surface acoustic wave (SAW) devices dominate high-frequency applications. Materials include quartz crystals, lithium niobate, lithium tantalate, lithium tetraborate, and new piezoelectric single crystals like La3Ga5SiO14 (LGS).

• Relaxor ferroelectric piezoelectric single crystals such as PMN-PT and PZN-PT have made significant advances in medical ultrasound imaging.

Other Advanced Functional Ceramics:

• Thin-film functional ceramics, PLZT transparent electro-optic ceramics, far-infrared ceramics, piezoelectric composites, magnetoelectric composites, ITO and ATO transparent conductive materials, fast ion conductor ceramics (e.g., SOFC and lithium-ion battery electrode materials), bioceramics, high-temperature superconducting ceramics, and nuclear reactor ceramics.

Research Hotspots:

1. Lead-Free Piezoelectric Ceramics:

With increasing environmental awareness, lead-free piezoelectric ceramics have become a major research focus. Researchers are exploring alternative materials such as bismuth-based and alkali metal-based ceramics to replace traditional lead zirconate titanate (PZT).

2. High-Performance Dielectric Materials:

Efforts are being made to develop dielectric materials with higher permittivity, lower losses, and better temperature stability to meet the demands of modern high-frequency and miniaturized electronic devices.

3. Microwave Dielectric Ceramics:

Research on microwave ceramic materials focuses on achieving high-frequency stability, low cost, and compatibility with multilayer processing techniques, especially for use in 5G communication and satellite technology.

4. Advanced Piezoelectric Single Crystals:

Relaxor ferroelectric single crystals like PMN-PT and PZN-PT are being further developed to improve their piezoelectric properties for applications in medical imaging and precision actuators.

5. **Multifunctional Composite Ceramics

(1) The performance of ceramics largely depends on the quality of raw powder materials. Advanced functional ceramics generally have the following requirements for raw powders:

a. High-purity compound-state content of the main components.

b. For composite oxide powders, a specific crystal phase is required, or the content of this phase must meet a minimum threshold.

c. Specific requirements for powder particle size and uniformity.

d. Stoichiometric ratios of elemental oxides in composite oxide powders.

e. Powder particles with a uniform and well-defined morphology.

(2) High-Performance Ceramic Energy Storage Dielectrics

Energy storage capacitors offer advantages such as high energy density, fast charge and discharge rates, resistance to cyclic aging, and stable performance in extreme conditions like high temperature and high voltage. They have broad application prospects in fields such as electric vehicles, power electronics, pulse power supplies, high-energy-density weapons, renewable energy, and smart grid systems.

(3) Dielectric Ceramics and Their Components

Miniaturization (including chip-scale packaging) is one of the key goals in current component development. Achieving this requires:

a. Enhancing the performance of ceramic materials.

b. Developing advanced manufacturing processes and technologies.

(4) Piezoelectric and Ferroelectric Ceramics and Their Components

Piezoelectric ceramics hold a prominent position in information functional ceramic materials. Piezoelectric actuators offer advantages such as high displacement control precision, rapid response, high driving force, low power consumption, and a wide operating frequency range. As a result, piezoelectric ceramics are widely used in electromechanical sensors and actuators. Components like resonators, filters, surface acoustic wave devices, and piezoelectric ceramic actuators play crucial roles in information technology.

(5) Environmentally Friendly Lead-Free Piezoelectric Ceramics

Currently, lead-free piezoelectric ceramics are mainly classified into three systems: BaTiO3, Na0.5Bi0.5TiO3, and K0.5Na0.5NbO3 (KNN). Among them, BaTiO3 and Na0.5Bi0.5TiO3 exhibit relatively lower piezoelectric performance and Curie temperature, primarily being used in ultrasonic detectors. KNN, with its lower sintering temperature, high Curie temperature, and high piezoelectric coefficient, shows potential to replace PZT as a viable alternative material.

(6) Multiferroics with Coexisting Ferroelectricity and Ferromagnetism, and Magnetoelectric Coupling

The trend towards miniaturization of components has increased research into multifunctional materials that integrate dielectric and magnetic properties. Multiferroic materials exhibit both ferroelectric/piezoelectric and ferromagnetic characteristics, and more importantly, they demonstrate magnetoelectric effects—such as magnetization induced by an electric field or polarization induced by a magnetic field. These materials offer significant potential for developing new information processing technologies and magnetoelectric sensor devices based on the integration of ferroelectric/piezoelectric and magnetic effects. Recently, this has become a cutting-edge research field internationally.

(7) Giant Electrocaloric Effect

The electrocaloric effect refers to the adiabatic temperature change or isothermal entropy change in polar materials caused by alterations in polarization states due to an external electric field. Reports on the electrocaloric effect date back to the 1930s, but due to the low operating electric field strength of ceramic materials, the observed adiabatic temperature changes were typically less than 1°C. In recent years, this area of research has seen rapid advancements.

(8) Emergence of Passive Integration Technology

The rise of passive integration technology, which integrates various passive electronic components (capacitors, inductors, resistors, sensors, antennas, etc.) into a single module via low-temperature co-fired ceramics (LTCC), has opened up new application areas for functional ceramics. At the same time, it has raised numerous scientific challenges in materials and fabrication, including:

• Development of new functional ceramic materials with both low sintering temperatures and high performance.

• Zero-shrinkage LTCC materials.

• RF/microwave LTCC materials.

• Techniques for forming and interconnecting internal electrodes in 3D and complex-structured ceramic devices.

• Low-cost tape-casting methods for high-density ultra-thin ceramic membranes.

• Controlling co-firing densification behaviors and interface compatibility in heterogeneous materials.

• Modeling, simulation, design principles, and performance optimization in integrated ceramic systems, including field distribution analysis.