[[Chemistry]] | [[18th Century]] | [[China]] | [[Japan]] | [[Germany]] | [[Sweden]] | [[Canada]] | [[Copper]] ## Overview Tellurium (Te), atomic number 52, is a brittle, silvery-white metalloid that sits in Group 16 of the periodic table — the chalcogens — directly below selenium and above polonium. It is one of the **rarest elements in the Earth's crust**, comparable in abundance to platinum and considerably rarer than gold, yet it has never commanded the mystique or market attention of precious metals because its applications, until recently, were niche and its public profile nonexistent. That obscurity is changing. Tellurium is the essential component of **cadmium telluride (CdTe) thin-film solar cells** — the technology platform of **First Solar**, the largest American solar manufacturer and the only major non-Chinese solar panel company competing at global scale. This single application has transformed tellurium from a metallurgical curiosity into a **strategic material for the energy transition**, tying its fortunes directly to the geopolitics of solar energy, U.S.-China technology competition, and the future of Western photovoltaic manufacturing independence. Tellurium's supply chain, like selenium's (its chalcogen sibling, discussed earlier in this series), is **entirely hostage to copper refining** — produced exclusively as a byproduct of copper anode slime processing, with no primary mines and no independent ability to scale supply in response to demand. This structural dependency, combined with geological rarity and a thin, opaque market, makes tellurium one of the most supply-constrained elements in the energy transition portfolio. --- ## Discovery & History Tellurium was discovered in **1782** by **Franz-Joseph Müller von Reichenstein**, an Austrian mining engineer working in the gold mining district of Transylvania (then part of the Habsburg Empire, now Romania). Müller encountered a puzzling metallic substance in gold ores from the Zlatna mine that he could not identify as any known element. He studied it intermittently for years but could not confirm its novelty with certainty. In **1798**, **Martin Heinrich Klaproth** — the same German chemist who identified zirconium and uranium — obtained samples from Müller, confirmed that the substance was indeed a new element, and named it **tellurium** from the Latin _tellus_, meaning **"Earth"**. This was the deliberate terrestrial counterpart to selenium's lunar name (_Selene_, the Moon) — though selenium would not be discovered for another two decades, making the eventual pairing a coincidence of naming convention rather than deliberate symmetry. Berzelius completed the poetic pair when he named selenium in 1817. Transylvania's connection to tellurium is not incidental. The region's gold deposits are among the few places on Earth where **native gold-telluride minerals** (calaverite, krennerite, sylvanite) occur in significant quantities — ores in which gold is chemically bonded to tellurium rather than occurring as free metal. The **Kalgoorlie gold rush** in Western Australia (1890s) encountered similar telluride gold ores, and the initial inability to extract gold from these unfamiliar minerals caused considerable frustration before appropriate metallurgical processes were developed. Tellurium's discovery is thus rooted in the geology of gold — a connection that persists in modern supply chains, where gold refining residues remain a secondary tellurium source. --- ## Key Properties - **Metalloid behavior** — Tellurium occupies the boundary between metals and nonmetals. It is brittle (shattering when struck, unlike true metals), a poor conductor of electricity in its pure form, but becomes a semiconductor when alloyed or compounded — properties that underpin its photovoltaic and thermoelectric applications. - **Narrow bandgap semiconductor** — Tellurium and its compounds (particularly CdTe) have bandgaps well-suited to solar energy conversion - **Thermoelectric properties** — Bismuth telluride (Bi₂Te₃) is the benchmark room-temperature thermoelectric material - **Alloying effects** — Small additions of tellurium dramatically improve the machinability of steel and copper alloys - **Toxicity** — Tellurium compounds are moderately toxic, and exposure produces a distinctive and extremely persistent **garlic-like body odor** (tellurium breath) that can last for weeks — one of the more memorable occupational health effects in chemistry. Even trace exposure produces this effect, making it an unusually sensitive biological indicator of tellurium contact. --- ## Key Applications ### Cadmium Telluride (CdTe) Solar Cells — The Defining Application This is the application that elevates tellurium from industrial footnote to strategic material. #### The Technology **CdTe thin-film photovoltaics** use a layer of cadmium telluride — just a few micrometers thick — as the light-absorbing semiconductor. CdTe's bandgap of ~1.5 eV is nearly optimal for single-junction solar energy conversion (close to the theoretical Shockley-Queisser efficiency peak for terrestrial solar spectra), and the material can be deposited rapidly and cheaply using vapor transport or close-space sublimation processes. CdTe thin-film solar offers several advantages over the dominant crystalline silicon (c-Si) technology: - **Lower energy payback time** — CdTe panels recover the energy used in their manufacture faster than silicon panels - **Superior performance in hot climates** — CdTe has a lower temperature coefficient of power loss, meaning it maintains efficiency better than silicon in high-temperature environments (deserts, tropical regions) - **Better performance in diffuse light** — CdTe performs relatively well under cloudy or hazy conditions - **Simpler, more integrated manufacturing** — CdTe panels can be manufactured from raw glass to finished module in a single integrated factory in approximately 3.5 hours, compared to the multi-step, multi-facility supply chain for silicon panels - **Lower water usage** in manufacturing than silicon #### First Solar — The Strategic Company **First Solar** (Tempe, Arizona) is the **world's dominant CdTe solar manufacturer** and one of the most strategically significant clean energy companies on Earth. Founded in 1999 and built on technology originally developed by **Solar Cells Inc.** (later acquired and commercialized), First Solar has grown into a company with a market capitalization frequently exceeding **$20 billion** and manufacturing capacity spanning the United States, Malaysia, Vietnam, and India (with a new U.S. factory in Alabama and expansion in Ohio and Louisiana). First Solar's strategic significance extends beyond its market position: 1. **The only major non-Chinese solar manufacturer at scale** — The global crystalline silicon solar supply chain is overwhelmingly Chinese, from polysilicon production (Tongwei, Daqo, GCL-Poly, TBEA — with significant production in Xinjiang, raising forced labor concerns) through wafer, cell, and module manufacturing. First Solar's CdTe technology represents the **only alternative solar manufacturing platform** that operates independently of the Chinese silicon supply chain. This makes First Solar a **de facto strategic asset** for Western energy security. 2. **Inflation Reduction Act beneficiary** — The IRA's domestic manufacturing tax credits (Section 45X) have been enormously beneficial to First Solar, which manufactures in the United States and sources materials from non-Chinese supply chains. First Solar's stock price surged following the IRA's passage, and the company has announced major U.S. manufacturing expansions. 3. **U.S. Department of Defense interest** — CdTe's independence from Chinese supply chains has attracted defense-sector interest for military microgrids, forward operating base power, and other applications where supply chain security is paramount. 4. **Cadmium concern** — CdTe panels contain cadmium, a toxic heavy metal. First Solar has invested heavily in **panel recycling programs** and lifecycle management to address environmental and regulatory concerns. The company operates collection and recycling programs for end-of-life panels, recovering cadmium and tellurium for reuse — a cradle-to-cradle model that is more advanced than the recycling infrastructure for silicon panels. #### The Efficiency Race CdTe's historical weakness has been lower efficiency than crystalline silicon — a gap that First Solar has been steadily closing. First Solar's current commercial modules achieve efficiencies in the **19–20%+ range**, with research cells exceeding **22%**. Crystalline silicon modules are typically in the **21–23% range** commercially, with laboratory records above 26%. While a gap remains, CdTe's cost advantages, manufacturing simplicity, and supply chain independence make it competitive on a **levelized cost of energy (LCOE)** basis — the metric that ultimately determines technology adoption in utility-scale solar markets. #### Tellurium Intensity and Demand A critical question for tellurium's future is **how much tellurium CdTe solar requires** and whether supply can support aggressive growth: - First Solar has progressively **reduced tellurium intensity** per watt of solar capacity through thinner absorber layers and higher efficiencies. Current CdTe modules use substantially less tellurium per watt than early generations. - Nevertheless, a significant scaling of CdTe manufacturing — as projected under IRA-driven U.S. solar expansion — requires corresponding growth in tellurium supply - First Solar has pursued a **vertical integration strategy for tellurium**, securing long-term supply agreements with copper refiners and investing in tellurium recycling from end-of-life panels. The company reportedly maintains strategic tellurium inventories. - Some analyses have identified tellurium availability as a **potential ceiling on CdTe market share** — the total amount of tellurium recoverable from copper refining may limit how large CdTe can grow as a fraction of the global solar market, even under optimistic supply scenarios. ### Thermoelectric Materials — Bismuth Telluride **Bismuth telluride (Bi₂Te₃)** and its alloys with antimony telluride (Sb₂Te₃) are the **benchmark thermoelectric materials** for applications near room temperature — devices that convert temperature differences directly into electricity (Seebeck effect) or pump heat using electricity (Peltier effect). Applications include: - **Thermoelectric coolers (TECs)** — Solid-state cooling devices used in: - Laser diode temperature stabilization (essential for fiber optic telecommunications) - Infrared detector cooling (military and scientific thermal imaging) - Medical and scientific instrument temperature control - Portable coolers and beverage chillers - Seat coolers in luxury vehicles - **Thermoelectric generators (TEGs)** — Recovering waste heat as electricity: - Automotive waste heat recovery (exhaust systems) - Remote power generation (oil and gas pipeline monitoring, space probes) - Industrial waste heat recovery - **Radioisotope thermoelectric generators (RTGs)** — Bismuth telluride elements (and lead telluride for higher temperatures) have been used in RTGs powering deep-space probes — Voyager 1 and 2, Cassini, New Horizons, and the Mars Curiosity and Perseverance rovers use thermoelectric elements to convert heat from plutonium-238 decay into electricity. While the specific thermoelectric materials in these RTGs are typically lead telluride or silicon-germanium for the high-temperature stages, bismuth telluride elements are used in lower-temperature stages and in terrestrial applications. The conceptual principle is shared. The thermoelectric market is growing as waste heat recovery and solid-state cooling gain importance, but it remains small compared to the potential scale of CdTe solar. Key thermoelectric manufacturers include **II-VI Incorporated (now Coherent)**, **Ferrotec**, **Laird Thermal Systems**, and **Marlow Industries (a subsidiary of II-VI/Coherent)**. ### Metallurgy — Free-Machining Alloys Tellurium's oldest industrial application is as a **machinability additive** in steel and copper alloys: - **Free-machining steel** — Adding 0.04–0.10% tellurium to leaded or resulphurized steel improves chip-breaking during machining, producing shorter, more manageable chips that clear the cutting zone efficiently. This reduces tool wear, improves surface finish, and increases machining productivity. - **Free-machining copper** — Tellurium-bearing copper (C14500) contains ~0.5% Te, dramatically improving machinability while maintaining electrical conductivity. Used for electrical connectors, switch components, and other precision-machined electrical parts. These metallurgical applications are mature, stable, and consume a meaningful fraction of tellurium production — though they face gradual pressure from lead-free machining alternatives. ### Phase-Change Memory and Data Storage Tellurium-containing **chalcogenide alloys** — particularly **germanium-antimony-tellurium (GeSbTe or GST)** — are the active material in: - **Rewritable optical discs** — CD-RW, DVD-RW, and Blu-ray RW formats use GST phase-change layers that switch between crystalline (reflective) and amorphous (less reflective) states under laser heating - **Phase-change random access memory (PCRAM / PCM)** — An emerging non-volatile memory technology that stores data as the structural state (crystalline vs. amorphous) of GST or similar chalcogenide alloys. **Intel and Micron's 3D XPoint (Optane)** memory technology — now discontinued by Intel but technologically significant — used a chalcogenide phase-change material. PCRAM offers potential advantages over flash memory in speed, endurance, and scalability, and remains an active area of research and development. ### Topological Insulators — Frontier Physics Bismuth telluride (Bi₂Te₃) and related tellurium compounds have been identified as **topological insulators** — exotic quantum materials that are electrically insulating in their bulk but conduct electricity on their surfaces via protected quantum states. Topological insulators are among the most active areas of condensed matter physics research, with potential applications in: - **Quantum computing** — Topological qubits, if realized, could be inherently error-resistant - **Spintronics** — Devices that exploit electron spin rather than charge for information processing - **Ultra-sensitive detectors** — Exploiting the unique surface conduction properties This is fundamental research rather than near-term commercial demand, but it positions tellurium at the frontier of quantum materials science alongside elements like niobium and yttrium. ### Rubber Vulcanization Tellurium compounds (particularly tellurium diethyldithiocarbamate, TDEC) are used as **vulcanization accelerators** in rubber processing — specifically for heat-resistant rubber formulations. This is a small but established application in automotive hoses, industrial belts, and other rubber products requiring thermal stability. --- ## Supply Chain & Geopolitics ### The Byproduct Constraint — Copper's Gift and Curse Tellurium's supply chain situation is **functionally identical to selenium's** — and for exactly the same reasons. Virtually all commercial tellurium is recovered from the **anode slimes** generated during electrolytic copper refining. When copper anodes are dissolved and refined copper is deposited on cathodes, tellurium (along with selenium, gold, silver, and platinum group metals) accumulates in the residue at the bottom of the electrolytic cells. This means: 1. **Tellurium supply is entirely governed by copper refining decisions**, not tellurium demand 2. **Not all copper refineries recover tellurium** — the additional processing equipment represents a capital investment that many refiners choose not to make, particularly when tellurium prices are low 3. **The global volume of tellurium recoverable from copper refining** represents a finite ceiling on supply, regardless of demand or price — estimated at roughly **1,500–2,000 tonnes per year** of theoretical maximum recovery if every copper refinery worldwide extracted tellurium from its anode slimes 4. **Actual annual production is significantly lower** — approximately **500–600 tonnes per year** — because many refineries do not recover tellurium, and recovery rates from those that do vary widely ### Production Geography Because tellurium follows copper refining, its production map mirrors the copper smelting and refining landscape: #### China China is the **world's largest tellurium producer**, estimated at **50–65% of global output**. This directly reflects China's position as the world's largest copper refiner. Chinese tellurium is recovered from copper refinery anode slimes at facilities across the country, with secondary processing and purification concentrated among specialty metals companies. Key Chinese producers include: - **Vital Materials** (formerly known as Vital Thin Film Materials) — Headquartered in Changsha, Hunan province. Arguably the single most important company in the global tellurium supply chain. Vital Materials is the **world's largest tellurium refiner**, processing tellurium from Chinese copper smelters and producing high-purity tellurium for CdTe solar cells, thermoelectric devices, and other applications. Vital has supply agreements with First Solar, making the relationship between an Arizona-based solar company and a Hunan-based tellurium refiner one of the more strategically significant bilateral dependencies in the energy transition. - **Various copper smelter-affiliated refiners** — Jiangxi Copper, Tongling Nonferrous, Jinchuan Group, and others recover tellurium as part of their copper refining operations #### Japan Japan's sophisticated copper refining industry recovers tellurium at several facilities: - **JX Nippon Mining & Metals (ENEOS Group)** — Major Japanese copper refiner and tellurium producer - **Mitsubishi Materials** — Significant copper refining and tellurium recovery - **Sumitomo Metal Mining** — Copper refining with tellurium recovery Japanese tellurium production benefits from Japan's high-quality refining infrastructure and long experience in specialty metals processing. #### Canada - **Teck Resources** trail operations in British Columbia have historically produced tellurium from lead-zinc refining residues - **Canadian copper refiners** (including Glencore's Horne smelter in Quebec, though it primarily produces copper) contribute to the supply chain #### Sweden and Europe - **Boliden** — The Swedish mining and smelting company recovers tellurium from its copper refining operations at the Rönnskär smelter, one of the most technologically advanced copper smelters in the world. Boliden's tellurium production is among the few significant European sources. - **Aurubis** (Germany) — Europe's largest copper refiner recovers selenium and other anode slime constituents but tellurium recovery varies #### United States U.S. tellurium production has **declined** along with domestic copper smelting capacity. The **ASARCO** refinery in Amarillo, Texas (owned by Grupo México) is one of the few remaining U.S. copper refineries, and its tellurium recovery contributes to domestic supply. However, the U.S. is a **net importer of tellurium**, relying primarily on Canadian and Chinese supply. ### Market Characteristics The tellurium market is one of the most extreme examples of a **critical micro-market**: - **Total global production: ~500–600 tonnes annually** — smaller than virtually any other industrial metal - **Market value: roughly $100–200 million** depending on prices — trivially small - **Prices are volatile and opaque** — tellurium has traded anywhere from **$20/kg to $400+/kg** over the past two decades, with prices driven by speculative interest, CdTe demand expectations, and copper refining economics - **No futures market or exchange trading** — bilateral contracts and dealer markets, with reference prices published by Argus Media, Asian Metal, and similar sources - **First Solar's demand** represents a significant fraction of the total market, giving the company outsized influence as both price-setter and supply chain organizer - **Inventory positions at individual refiners** can move the market — the market is thin enough that a single large purchase or sale creates visible price effects ### The Tellurium Ceiling Problem The most fundamental strategic question about tellurium is whether **physically enough exists** to support aggressive growth of CdTe solar: #### The Optimistic View - First Solar has continuously **reduced tellurium intensity per watt** through thinner absorber layers and higher module efficiency, meaning each tonne of tellurium produces more solar capacity than it did a decade ago - **Not all copper refineries currently recover tellurium** — equipping more refineries with tellurium extraction could meaningfully increase supply within the existing copper production base - **Copper production itself is growing** (driven by electrification and the energy transition), which will increase the total anode slime volume from which tellurium can be recovered - **Recycling of end-of-life CdTe panels** will create a secondary tellurium supply stream (First Solar's recycling program is already operational) - **Selenium-tellurium substitution** — research into cadmium selenide-telluride (CdSeTe) alloys reduces the tellurium fraction required per cell #### The Pessimistic View - Even at maximum theoretical recovery from all global copper refining, annual tellurium supply would be roughly **1,500–2,000 tonnes** — a hard ceiling set by copper production - At current tellurium intensity, this supply supports CdTe manufacturing at a scale that remains a **single-digit percentage of the total global solar market** — significant but not dominant - If CdTe were to attempt to capture, say, 20–30% of global solar installations (hundreds of GW annually), tellurium supply would be insufficient under any realistic recovery scenario - **Copper concentrate grade decline** — as copper ore grades fall and mining shifts to different deposit types, the tellurium content of copper concentrates may not remain constant - **Competing demand** from thermoelectric, metallurgical, and emerging technology applications reduces the tellurium available for solar The reality likely lies in between: CdTe solar will continue to grow — strongly supported by the IRA, First Solar's manufacturing expansion, and CdTe's non-Chinese supply chain advantages — but tellurium availability will constrain CdTe's **ultimate market share ceiling** as a fraction of total global solar deployment. CdTe is likely to remain a **strategically important but minority technology** in a solar market overwhelmingly dominated by crystalline silicon. ### First Solar's Supply Chain Strategy First Solar's approach to tellurium supply security is one of the most sophisticated raw material strategies of any clean energy company: - **Long-term offtake agreements** with copper refiners for tellurium supply - **Strategic inventory management** — maintaining significant tellurium stockpiles to buffer against supply disruptions - **Recycling program** — recovering tellurium (and cadmium) from end-of-life panels, creating a circular supply stream that will grow as early-generation panels are decommissioned - **Material intensity reduction** — continuous R&D to reduce tellurium consumption per watt through thinner absorber layers and compositional optimization - **Supply chain diversification** — sourcing from multiple refiners across multiple countries to avoid single-source dependency - **Vertical integration consideration** — First Solar's deep involvement in tellurium supply chain management effectively makes it a specialty metals company as much as a solar manufacturer --- ## Environmental and Health Dimensions ### Cadmium Concerns in CdTe Solar The presence of **cadmium** in CdTe solar panels has been a persistent concern and a competitive talking point from the silicon solar industry: - **Manufacturing safety** — CdTe manufacturing involves handling cadmium compounds, requiring strict occupational health controls. First Solar's factories implement comprehensive containment and monitoring systems. - **Installed panel safety** — CdTe in finished panels is encapsulated in glass and polymer, making cadmium release during normal operation negligible. Fire testing and breakage studies indicate minimal environmental release under realistic scenarios. - **End-of-life management** — The primary concern is what happens when panels reach end-of-life in 25–30+ years. Without proper recycling, landfill disposal could eventually leach cadmium into groundwater. First Solar's pre-funded recycling program addresses this more proactively than any other solar manufacturer. - **Regulatory status** — CdTe solar panels are exempt from the EU's **Restriction of Hazardous Substances (RoHS) Directive** due to lifecycle analysis showing that the environmental benefits of solar energy generation outweigh the risks of encapsulated cadmium. This exemption has been periodically challenged but consistently upheld. The broader perspective: **CdTe solar panels contain less cadmium per unit of electricity generated over their lifetime than coal power plants release per unit of electricity** (coal fly ash contains cadmium). The comparative lifecycle analysis overwhelmingly favors CdTe solar, but the "cadmium in solar panels" narrative persists in public discourse. ### Tellurium Toxicity Tellurium compounds are **moderately toxic**: - **Tellurium breath** — The most distinctive effect. Even trace exposure to tellurium (through skin contact, inhalation, or ingestion) causes the body to metabolize tellurium into dimethyl telluride, producing an intensely **garlic-like odor** on the breath, in sweat, and in urine that can persist for **weeks to months**. This effect is so sensitive and so persistent that workers in tellurium-handling facilities can be identified by smell alone — an involuntary and socially impactful occupational marker. - **Organ toxicity** — Higher exposures cause nausea, central nervous system effects, and potentially liver and kidney damage, though acute tellurium poisoning is rare - **Environmental** — Tellurium is not a significant environmental pollutant due to its rarity and limited industrial discharge --- ## Tellurium and Gold — The Geological Connection Tellurium's original discovery context — Transylvanian gold ores — reflects a genuine geological association that persists in modern mining: - **Gold telluride minerals** (calaverite AuTe₂, krennerite AuTe₂, sylvanite AuAgTe₄) are found in specific types of **epithermal gold deposits** — particularly alkaline and low-sulfidation systems - Major gold-telluride deposits include **Cripple Creek (Colorado)**, **Kalgoorlie (Western Australia)**, **Emperor mine (Fiji)**, and **Săcărâmb (Romania, near the original discovery locality)** - **Gold refining** produces small quantities of tellurium as a byproduct, supplementing the primary copper-refining source - Some researchers have proposed that gold-telluride deposits could be developed as **co-product tellurium sources**, though the economics depend on gold prices and tellurium recovery technology --- ## Strategic Assessment Tellurium's geopolitical profile is shaped by a unique combination of factors: ### Extreme Vulnerabilities 1. **Geological rarity** — One of the rarest elements in the crust, comparable to platinum 2. **Complete byproduct dependency** — No primary mines; supply follows copper refining, not tellurium demand 3. **Hard supply ceiling** — Maximum recoverable tellurium from global copper refining is physically limited to ~1,500–2,000 tonnes/year 4. **Chinese refining dominance** — 50–65% of global production, with Vital Materials as the dominant refiner 5. **Critical dependency of First Solar** — The most strategically important non-Chinese solar manufacturer depends on a material predominantly refined in China 6. **Micro-market fragility** — A market so small that individual corporate decisions visibly move supply and price ### Strategic Importance 1. **CdTe solar = Western solar manufacturing independence** — Tellurium's significance derives largely from the fact that CdTe is the only solar technology that offers a non-Chinese supply chain path 2. **IRA-driven demand growth** — U.S. solar manufacturing expansion under the IRA directly increases tellurium demand 3. **Thermoelectric applications** in waste heat recovery and solid-state cooling are growing 4. **Quantum materials frontier** — Topological insulator research positions tellurium at the edge of next-generation physics and computing ### Mitigating Factors - First Solar's sophisticated supply chain management and recycling programs - Tellurium intensity per watt continues to decline - Copper production growth will gradually increase the anode slime base - Multiple copper-refining countries (Japan, Canada, Sweden, U.S.) can recover tellurium independently of China, even if China currently dominates volume --- ## Summary Tellurium is an element whose strategic significance is almost entirely mediated through a single company and a single technology — First Solar and CdTe thin-film photovoltaics. This is not a weakness of tellurium's importance but a reflection of how concentrated strategic value can become: in a solar market dominated by Chinese crystalline silicon, the only globally competitive non-Chinese alternative depends on one of the rarest elements on Earth, produced as a byproduct of an entirely different metal's refining, predominantly processed in the very country whose supply chain dominance it exists to circumvent. The circularity of this dependency — Western solar independence requiring a material refined in China — captures the essential paradox of critical mineral geopolitics in miniature. Tellurium's geological rarity imposes a hard ceiling on CdTe's ultimate market share, but within that ceiling, the technology fills a strategic role that no other solar platform currently occupies. Named for the Earth by Klaproth in 1798, tellurium has spent two centuries in geological obscurity only to emerge, in the third decade of the 21st century, as a material upon which the question of who manufactures the world's solar panels — and thus who controls the infrastructure of decarbonization — partially depends. For an element rarer than gold, that is a weight of consequence few would have predicted.