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High Efficiency End-Pumped Ho:Tm:YLF Disk Amplifier

Space based coherent lidar for global wind measurement requires an all solid state laser system with high energy, high efficiency and narrow linewidth that operates in the eye safe region. A Q-switched, diode pumped Ho:Tm:YLF 2 micrometer laser with output energy of as much as 125 mJ at 6 Hz with an optical-to-optical efficiency of 3% has been reported. Single frequency operation of the laser was achieved by injection seeding. The design of this laser is being incorporated into NASA's SPARCLE (SPAce Readiness Coherent Lidar Experiment) wind lidar mission. Laser output energy ranging from 500 mJ to 2 J is required for an operational space coherent lidar. We previously developed a high energy Ho:Tm:YLF master oscillator and side pumped power amplifier system and demonstrated a 600-mJ single frequency pulse at a repetition rate of 10 Hz. Although the output energy is high, the optical-to-optical efficiency is only about 2%. Designing a high energy, highly efficient, conductively cooled 2-micrometer laser remains a challenge. In this paper, the preliminary result of an end-pumped amplifier that has a potential to provide a factor 3 of improvement in the system efficiency is reported.

Yu, Jirong↗

Dense gas and HII regions in the starburst galaxy NGC 253

The energetic activity in the nuclear barred region of NGC 253 is attributable to a burst of star formation. NGC 253 is in many ways a twin of the prototypical starburst galaxy M82; the strong non-thermal radio continuum, high far-infrared luminosity, and bright molecular emission of the central 1 Kpc parallel the morphology of the M82 starburst. Furthermore, the filamentary low ionization optical emission and extended x ray emission along the minor axis in NGC 253 is similar to a scaled down version of the well developed galactic bipolar wind in M82. The infrared luminosity of NGC 253, 3(exp 10) solar luminosity, is comparable to M82 but is emitted from a smaller region (Telesco and Harper 1980). This suggests that the NGC 253 starburst may be more intense and at an earlier evolutionary stage than M82. However, the presence of a non-stellar AGN in NGC 253 may complicate the comparison (Turner and Ho, 1985). Researchers used the Hat Creek millimeter interferometer to map emission from the J = 1 to 0 transitions of HCN and HCO(+) as well as 3 mm continuum emission, toward the nuclear region of NGC 253. The HCO(+) and continuum observations are sensitive to spatial scales from 6 to 45 seconds. The 2 minute field of view comfortably includes the entire starburst region (about 40 seconds; 650 pc). Because the longer baseline HCN observations are not yet complete, they are only sensitive to spatial scales from 15 to 45 seconds.

Carlstrom, J. E.↗

Materials Data on Rb3HoO3 by Materials Project

Rb3HoO3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 1-coordinate geometry to five O2- atoms. There are a spread of Rb–O bond distances ranging from 2.68–3.21 Å. In the second Rb1+ site, Rb1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are two shorter (2.84 Å) and two longer (3.24 Å) Rb–O bond lengths. In the third Rb1+ site, Rb1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are two shorter (2.93 Å) and two longer (3.21 Å) Rb–O bond lengths. Ho3+ is bonded to four O2- atoms to form edge-sharing HoO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.11–2.19 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Rb1+ and two equivalent Ho3+ atoms. In the second O2- site, O2- is bonded in a 7-coordinate geometry to six Rb1+ and one Ho3+ atom.

36 MATERIALS SCIENCE↗

2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

Carbon dioxide (CO2) has been recognized as one of the most important greenhouse gases. It is essential for the study of global warming to accurately measure the CO2 concentration in the atmosphere and continuously record its variation. A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed in NASA Langley Research Center. This laser system is capable of making a vertical profiling of CO2 from ground and column measurement of CO2 from air and space-borne platform. The transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of ~50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. A Ho:YLF laser operating in the range of 2.05 micrometers can be tuned over several characteristic lines of CO2 absorption. Experimentally, a diode pumped Ho:Tm:YLF laser has been successfully used as the transmitter of coherent differential absorption lidar for the measurement of CO2 with a repetition rate of 5 Hz and pulse energy of 75 mJ. For coherent detection, high repetition rate is required for speckle averaging to obtain highly precise measurements. However, a diode pumped Ho:Tm:YLF laser can not operate in high repetition rate due to the large heat loading and up-conversion. A Tm:fiber laser pumped Ho:YLF laser with low heat loading can operate in high repetition rate. A theoretical model has been established to simulate the performance of Tm:fiber laser pumped Ho:YLF lasers. For continuous wave (CW) operation, high pump intensity with small beam size is suitable for high efficiency. For Q-switched operation, the optimal energy extraction relies on the pump intensity, pump volume, and pump duration which is inversely proportion to the repetition rate. CW and Q-switched Ho:YLF lasers with different linear cavity configurations have been designed and demonstrated for a 30 W Tm:fiber pump laser. The CW Ho laser slope efficiency and optical-to-optical efficiencies reach 65% and 55%, respectively. The pulsed laser efficiency depends on the repetition rate. For 1 kHz operation, the optical-to-optical efficiency is 39% when the pump power is 14.5W. Currently, the injection seeding success rate is between 99.4% and 99.95%. After a ten thousand pulses, the standard deviation of the laser frequency jitter is about 3 MHz. It meets the requirements of highly precise CO2 concentration measurement. In conclusion, an injection seeded, high repetition rate, Q-switched Ho:YLF laser has been developed for a coherent CO2 differential absorption lidar. This master-slave laser system has high optical-to-optical efficiency and seeding success rate. It can potentially meet the requirements of the coherent detection of CO2 concentration by a differential absorption lidar technique.

Singh, Upendra N.↗

Materials Data on Ho2Te4O11 by Materials Project

Ho2Te4O11 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.26–2.57 Å. There are two inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 3-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–2.57 Å. In the second Te4+ site, Te4+ is bonded in a distorted see-saw-like geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.87–2.32 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Te4+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two Te4+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ho3+ and one Te4+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Te4+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Te4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Te4+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Cs3HoO3 by Materials Project

Cs3HoO3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to five O2- atoms. There are a spread of Cs–O bond distances ranging from 2.87–3.37 Å. In the second Cs1+ site, Cs1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are two shorter (2.99 Å) and two longer (3.40 Å) Cs–O bond lengths. In the third Cs1+ site, Cs1+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are two shorter (3.12 Å) and two longer (3.27 Å) Cs–O bond lengths. Ho3+ is bonded to four O2- atoms to form edge-sharing HoO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.13–2.21 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Cs1+ and two equivalent Ho3+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to six Cs1+ and one Ho3+ atom.

36 MATERIALS SCIENCE↗

Mechanism and Kinetics of Ethanol–Acetaldehyde Conversion to 1,3-Butadiene over Isolated Lewis Acid La Sites in Silanol Nests in Dealuminated Beta Zeolite

Biomass-derived ethanol (EtOH) and acetaldehyde (AcH) conversion to 1,3-butadiene (1,3-BD) is an alternative process for 1,3-BD production. The present investigation reports the preparation and characterization of isolated La sites introduced into the silanol nests in DeAlBEA as well as detailed studies of the mechanism and kinetics for the conversion of an EtOH-AcH mixture to 1,3-BD. La sites supported on DeAlBEA are found to be present as (≡SiO) 2 La-OH groups that are H-bonded with adjacent Si-OH groups, possessing high C-C coupling activity and stability, superior to state-of-the-art Y-DeAlBEA. La sites supported on silica (La-SiO 2 ) with a similar chemical structure but no H-bonding interaction with Si-OH groups were prepared for comparison. Lewis acid La sites promote AcH aldol condensation, and the activity of such sites is nearly identical for both La-DeAlBEA and La-SiO 2 . Further, the rate of C 4 product formation increases by a factor of 4.8 upon addition of EtOH to the feed of AcH over La-DeAlBEA, whereas that over La/SiO 2 remains unchanged. Investigation of the mechanism and kinetics of AcH aldol condensation and EtOH-AcH conversion to 1,3-BD revealed two C-C bond forming pathways-AcH aldol condensation by Lewis acid La sites and direct coupling of EtOH-AcH over H-bonded (≡SiO) 2 La-OH···HO-Si≡ sites. This study provides important information about the role of the local environment of isolated Lewis acid sites and their effects on the direct coupling of EtOH and AcH to form 1,3-BD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Materials Data on Ho3ReO8 by Materials Project

Ho3ReO8 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with three equivalent ReO6 octahedra, corners with three equivalent HoO7 pentagonal bipyramids, an edgeedge with one ReO6 octahedra, and a faceface with one HoO7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 49–60°. There are a spread of Ho–O bond distances ranging from 2.24–2.41 Å. In the second Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ho–O bond distances ranging from 2.36–2.44 Å. In the third Ho3+ site, Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with three equivalent ReO6 octahedra, corners with three equivalent HoO7 pentagonal bipyramids, an edgeedge with one ReO6 octahedra, and a faceface with one HoO7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 46–58°. There are a spread of Ho–O bond distances ranging from 2.24–2.42 Å. Re7+ is bonded to six O2- atoms to form ReO6 octahedra that share corners with six HoO7 pentagonal bipyramids and edges with two HoO7 pentagonal bipyramids. There are a spread of Re–O bond distances ranging from 1.84–1.95 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Re7+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Re7+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Ho3+ and one Re7+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Re7+ atom. In the fifth O2- site, O2- is bonded to four Ho3+ atoms to form a mixture of distorted corner and edge-sharing OHo4 tetrahedra. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Re7+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ce(HoS2)3 by Materials Project

Ce(HoS2)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with three HoS6 octahedra, edges with two equivalent HoS6 octahedra, and edges with four equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 39–50°. There are a spread of Ho–S bond distances ranging from 2.69–2.93 Å. In the second Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, a cornercorner with one HoS7 pentagonal bipyramid, edges with four equivalent HoS6 octahedra, and edges with two equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 54–62°. There are a spread of Ho–S bond distances ranging from 2.66–2.77 Å. In the third Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, corners with two equivalent HoS7 pentagonal bipyramids, and edges with four equivalent HoS6 octahedra. The corner-sharing octahedra tilt angles range from 54–62°. There are a spread of Ho–S bond distances ranging from 2.66–2.79 Å. Ce3+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Ce–S bond distances ranging from 2.90–3.04 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to four Ho3+ atoms. In the second S2- site, S2- is bonded to three Ho3+ and one Ce3+ atom to form distorted SCeHo3 trigonal pyramids that share corners with two equivalent SCe2Ho3 square pyramids, corners with four SCe2Ho3 trigonal bipyramids, corners with two equivalent SCeHo3 trigonal pyramids, edges with three equivalent SCe2Ho3 square pyramids, and edges with two equivalent SCe3Ho2 trigonal bipyramids. In the third S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the fourth S2- site, S2- is bonded to three equivalent Ho3+ and two equivalent Ce3+ atoms to form distorted SCe2Ho3 square pyramids that share corners with six SCe2Ho3 trigonal bipyramids, corners with two equivalent SCeHo3 trigonal pyramids, edges with four equivalent SCe2Ho3 square pyramids, edges with two SCe2Ho3 trigonal bipyramids, and edges with three equivalent SCeHo3 trigonal pyramids. In the fifth S2- site, S2- is bonded to three Ho3+ and two equivalent Ce3+ atoms to form distorted SCe2Ho3 trigonal bipyramids that share corners with two equivalent SCe2Ho3 square pyramids, corners with two equivalent SCe3Ho2 trigonal bipyramids, corners with three equivalent SCeHo3 trigonal pyramids, an edgeedge with one SCe2Ho3 square pyramid, and edges with five SCe2Ho3 trigonal bipyramids. In the sixth S2- site, S2- is bonded to two equivalent Ho3+ and three equivalent Ce3+ atoms to form distorted SCe3Ho2 trigonal bipyramids that share corners with four equivalent SCe2Ho3 square pyramids, corners with two equivalent SCe2Ho3 trigonal bipyramids, a cornercorner with one SCeHo3 trigonal pyramid, an edgeedge with one SCe2Ho3 square pyramid, edges with seven SCe2Ho3 trigonal bipyramids, and edges with two equivalent SCeHo3 trigonal pyramids.

36 MATERIALS SCIENCE↗

Materials Data on Na3HoBr6 by Materials Project

Na3HoBr6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six Br1- atoms to form NaBr6 octahedra that share corners with six equivalent HoBr6 octahedra. The corner-sharing octahedra tilt angles range from 40–45°. There are a spread of Na–Br bond distances ranging from 2.91–3.07 Å. In the second Na1+ site, Na1+ is bonded in a 5-coordinate geometry to seven Br1- atoms. There are a spread of Na–Br bond distances ranging from 2.99–3.69 Å. Ho3+ is bonded to six Br1- atoms to form HoBr6 octahedra that share corners with six equivalent NaBr6 octahedra. The corner-sharing octahedra tilt angles range from 40–45°. There are a spread of Ho–Br bond distances ranging from 2.78–2.82 Å. There are three inequivalent Br1- sites. In the first Br1- site, Br1- is bonded to three Na1+ and one Ho3+ atom to form a mixture of distorted edge and corner-sharing BrNa3Ho trigonal pyramids. In the second Br1- site, Br1- is bonded to three Na1+ and one Ho3+ atom to form a mixture of distorted edge and corner-sharing BrNa3Ho trigonal pyramids. In the third Br1- site, Br1- is bonded in a 3-coordinate geometry to four Na1+ and one Ho3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ho3Sb5O12 by Materials Project

Ho3Sb5O12 crystallizes in the cubic I-43m space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.25 Å) and four longer (2.60 Å) Ho–O bond lengths. There are two inequivalent Sb3+ sites. In the first Sb3+ site, Sb3+ is bonded in a 3-coordinate geometry to three equivalent O2- atoms. All Sb–O bond lengths are 2.04 Å. In the second Sb3+ site, Sb3+ is bonded in a 4-coordinate geometry to four O2- atoms. There are two shorter (1.99 Å) and two longer (2.23 Å) Sb–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two Sb3+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Sb3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ho5B2(O2F3)3 by Materials Project

Ho5B2(O2F3)3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 9-coordinate geometry to four O2- and five F1- atoms. There are a spread of Ho–O bond distances ranging from 2.33–2.56 Å. There are a spread of Ho–F bond distances ranging from 2.21–2.41 Å. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to three O2- and five F1- atoms. There are a spread of Ho–O bond distances ranging from 2.31–2.41 Å. There are a spread of Ho–F bond distances ranging from 2.23–2.51 Å. In the third Ho3+ site, Ho3+ is bonded in a 9-coordinate geometry to four O2- and five F1- atoms. There are two shorter (2.34 Å) and two longer (2.36 Å) Ho–O bond lengths. There are a spread of Ho–F bond distances ranging from 2.28–2.64 Å. B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.38–1.40 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to three Ho3+ and one B3+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to three Ho3+ and one B3+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three Ho3+ and one B3+ atom. There are five inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the second F1- site, F1- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the third F1- site, F1- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the fifth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on Ho3TaO7 by Materials Project

Ho3TaO7 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are six inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six O2- atoms to form distorted HoO6 octahedra that share corners with two equivalent HoO6 octahedra and corners with two TaO4 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Ho–O bond distances ranging from 2.16–2.40 Å. In the second Ho3+ site, Ho3+ is bonded to six O2- atoms to form distorted HoO6 octahedra that share corners with two equivalent HoO6 octahedra and corners with two TaO4 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Ho–O bond distances ranging from 2.17–2.41 Å. In the third Ho3+ site, Ho3+ is bonded in a 5-coordinate geometry to six O2- atoms. There are a spread of Ho–O bond distances ranging from 2.15–2.72 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 5-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.15–2.80 Å. In the fifth Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.13–2.71 Å. In the sixth Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.13–2.68 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to four O2- atoms to form distorted TaO4 tetrahedra that share corners with two HoO6 octahedra and a cornercorner with one TaO5 tetrahedra. The corner-sharing octahedra tilt angles range from 60–63°. There is two shorter (1.90 Å) and two longer (1.91 Å) Ta–O bond length. In the second Ta5+ site, Ta5+ is bonded to five O2- atoms to form distorted TaO5 tetrahedra that share corners with two HoO6 octahedra and a cornercorner with one TaO4 tetrahedra. The corner-sharing octahedra tilt angles range from 61–63°. There are a spread of Ta–O bond distances ranging from 1.90–2.47 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to four Ho3+ atoms to form corner-sharing OHo4 tetrahedra. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ho3+ atoms. In the third O2- site, O2- is bonded to four Ho3+ atoms to form corner-sharing OHo4 tetrahedra. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two Ho3+ and one Ta5+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Ta5+ atom. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Ta5+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ho3+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Ta5+ atom. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and two Ta5+ atoms. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Ta5+ atom. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Ta5+ atom. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Ta5+ atom. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Ho3+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on Ho2VPO8 by Materials Project

Ho2VPO8 is Zircon-derived structured and crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.37 Å) and four longer (2.39 Å) Ho–O bond lengths. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are four shorter (2.26 Å) and four longer (2.44 Å) Ho–O bond lengths. V5+ is bonded in a tetrahedral geometry to four equivalent O2- atoms. All V–O bond lengths are 1.73 Å. P5+ is bonded in a tetrahedral geometry to four equivalent O2- atoms. All P–O bond lengths are 1.56 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Ho3+ and one P5+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one V5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ho3Si3O10F by Materials Project

Ho3Si3O10F crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to six O2- and one F1- atom. There are a spread of Ho–O bond distances ranging from 2.29–2.58 Å. The Ho–F bond length is 2.24 Å. In the second Ho3+ site, Ho3+ is bonded to six O2- and one F1- atom to form HoO6F pentagonal bipyramids that share corners with six SiO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.23–2.46 Å. The Ho–F bond length is 2.39 Å. In the third Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six O2- and one F1- atom. There are a spread of Ho–O bond distances ranging from 2.25–2.73 Å. The Ho–F bond length is 2.29 Å. There are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent HoO6F pentagonal bipyramids and a cornercorner with one SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.64–1.68 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent HoO6F pentagonal bipyramids and corners with two SiO4 tetrahedra. There is two shorter (1.63 Å) and two longer (1.66 Å) Si–O bond length. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent HoO6F pentagonal bipyramids and a cornercorner with one SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.62–1.67 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and two Si4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Si4+ atoms. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Si4+ atom. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Si4+ atom. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Si4+ atom. F1- is bonded in a 3-coordinate geometry to three Ho3+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on HoTaO4 by Materials Project

HoTaO4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.30–2.46 Å. Ta5+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ta–O bond distances ranging from 1.88–2.36 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two equivalent Ta5+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Ta5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ho2WO6 by Materials Project

Ho2WO6 crystallizes in the orthorhombic P2_12_12_1 space group. The structure is three-dimensional. there are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.24–2.78 Å. In the second Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.22–2.44 Å. In the third Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.23–2.74 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Ho–O bond distances ranging from 2.21–2.60 Å. There are two inequivalent W6+ sites. In the first W6+ site, W6+ is bonded in a distorted octahedral geometry to six O2- atoms. There are a spread of W–O bond distances ranging from 1.87–2.15 Å. In the second W6+ site, W6+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of W–O bond distances ranging from 1.92–2.02 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one W6+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one W6+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one W6+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one W6+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one W6+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one W6+ atom. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to three Ho3+ and one W6+ atom. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to three Ho3+ and one W6+ atom. In the ninth O2- site, O2- is bonded in a distorted tetrahedral geometry to three Ho3+ and one W6+ atom. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to three Ho3+ and one W6+ atom. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to three Ho3+ and one W6+ atom. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one W6+ atom.

36 MATERIALS SCIENCE↗

Machine learning-accelerated discovery of iron cobalt phosphides as rare-earth-free magnets

Here, the discovery of rare-earth-free permanent magnets has been a goal of scientists for decades. The absence of rare-earth elements will alleviate a pressing concern about the availability of rare-earth elements used in permanent magnets. These magnets are crucial for applications such as wind turbines, electric cars, and memory devices. Rare-earth magnets are special owing to a large magnetic anisotropy energy (K 1 ). In contrast, iron cobalt phosphides hold promise since doping P into cubic FeCo can induce anisotropy, leading to a large coercivity, without introducing rare-earth elements. We present a comprehensive search over the Fe-Co-P ternary space for magnets, utilizing recently developed adaptive machine learning feedback to efficiently screen over 850 000 structures. We focus on machine learning acceleration as a paradigm for materials design. Further adaptive genetic algorithm searches and first-principles calculations aid in the identification of 16 new structures below the known convex hull. Five of them possess high magnetic polarization (J s > 1 T). The structures with desirable magnetic properties center on (Fe,Co) 2⁢ P. This supports conventional wisdom, which focuses on the mixture of the two known end compounds: Fe 2 ⁢P and Co 2 ⁢P. Our work provides guidance for synthesis. We find Fe 7 ⁢CoP 4 shows the most promise (J s = 1.03T and K 1 = 0.83MJ/m 3 ).

36 MATERIALS SCIENCE↗